Process for making nitriles

ABSTRACT

An improved multi-reaction zone process provides for improved nitrile product quality and yield. In a first reaction zone, 1,3-butadiene is reacted with hydrogen cyanide in the presence of a catalyst to produce pentenenitriles comprising 3-pentenenitrile and 2-methyl-3-butenenitrile. In a second reaction zone, 2-methyl-3-butenenitrile, recovered from the first reaction zone, is isomerized to 3-pentenenitrile. In an optional third reaction zone, 3-pentenenitrile recovered from the first and second reaction zones is reacted with hydrogen cyanide in the presence of a catalyst and a Lewis acid to produce adiponitrile. A portion of the first catalyst is purified and recycled. Zero valent nickel is added to the purified first catalyst before it is recycled.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 371 application of PCT/US11/40656, filed on Jun.16, 2011, which claims the benefit of U.S. Provisional Application No.61/362,175, filed Jul. 7, 2010.

FIELD OF THE INVENTION

This disclosure relates to a process for manufacturing nitriles. Moreparticularly, the disclosure relates to an improved multi-reaction zoneprocess to provide for improved nitrile product quality and yield. In afirst reaction zone, 1,3-butadiene is reacted with hydrogen cyanide inthe presence of a catalyst to produce pentenenitriles comprising3-pentenenitrile and 2-methyl-3-butenenitrile. In a second reactionzone, 2-methyl-3-butenenitrile, recovered from the first reaction zone,is isomerized to 3-pentenenitrile. In an optional third reaction zone,3-pentenenitrile recovered from the first and second reaction zones isreacted with hydrogen cyanide in the presence of a catalyst and a Lewisacid to produce adiponitrile. A portion of the first catalyst ispurified and recycled. Zero valent nickel is added to the purified firstcatalyst before it is recycled.

BACKGROUND OF THE INVENTION

Adiponitrile (ADN) is a commercially important and versatileintermediate in the industrial production of nylon polyamides useful informing films, fibers, and molded articles. ADN may be produced byhydrocyanation of 1,3-butadiene (BD) in the presence of transition metalcomplexes comprising various phosphorus-containing ligands. For example,catalysts comprising zero-valent nickel and monodentatephosphorus-containing ligands are well documented in the prior art; see,for example, U.S. Pat. Nos. 3,496,215; 3,631,191; 3,655,723 and3,766,237; and Tolman, C. A., McKinney, R. J., Seidel, W. C., Druliner,J. D., and Stevens, W. R., Advances in Catalysis, 1985, Vol. 33, pages1-46. Improvements in the hydrocyanation of ethylenically unsaturatedcompounds with catalysts comprising zero-valent nickel and certainmultidentate phosphite ligands are also disclosed; e.g., see: U.S. Pat.Nos. 5,512,696; 5,821,378; 5,959,135; 5,981,772; 6,020,516; 6,127,567;and 6,812,352.

3-Pentenenitrile (3PN) may be formed through a series of reactions asillustrated below.

According to abbreviations used herein, BD is 1,3-butadiene, HC≡N ishydrogen cyanide, and 2M3BN is 2-methyl-3-butenenitrile. A method toincrease the chemical yield of 3PN from BD hydrocyanation includes thecatalytic isomerization of 2M3BN to 3PN (Equation 2 above) in thepresence of NiL₄ complexes as disclosed in U.S. Pat. No. 3,536,748.Co-products of BD hydrocyanation and 2M3BN isomerization may include4-pentenenitrile (4PN), 2-pentenenitrile (2PN), 2-methyl-2-butenenitrile(2M2BN), and 2-methylglutaronitrile (MGN).

In the presence of transition metal complexes comprising variousphosphorus-containing ligands, dinitriles such as ADN, MGN, andethylsuccinonitrile (ESN) may be formed by the hydrocyanation of 3PN and2M3BN, as illustrated in Equations 3 and 4 below. Equation 4 also showsthat 2M2BN can be formed when 2M3BN undesirably isomerizes in thepresence of a Lewis acid promoter that may be carried over from apentenenitrile hydrocyanation reaction zone.

The hydrocyanation of activated olefins such as conjugated olefins(e.g., 1,3-butadiene) can proceed at useful rates without the use of aLewis acid promoter. However, the hydrocyanation of un-activatedolefins, such as 3PN, require at least one Lewis acid promoter to obtainindustrially useful rates and yields for the production of linearnitriles, such as ADN. For example, U.S. Pat. Nos. 3,496,217, 4,874,884,and 5,688,986 disclose the use of Lewis acid promoters for thehydrocyanation of non-conjugated ethylenically unsaturated compoundswith nickel catalysts comprising phosphorous-containing ligands.

An integrated process for the production of ADN from BD and HC≡N cancomprise BD hydrocyanation, 2M3BN isomerization to produce 3PN, and thehydrocyanation of pentenenitriles, including 3PN, to produce ADN andother dinitriles. Integrated processes are disclosed, for example, inUnited States Patent Application 2009/0099386 A1.

Disclosed in United States Patent Publication No. 2007/0260086, is aprocess for the preparation of dinitriles with an aim to provide for therecovery of a catalyst formed by a mixture of mono- and bidentateligands and to be able to reuse the catalyst thus recovered in thehydrocyanation and/or isomerization stages.

United States Patent Publication No. 2008/0221351 discloses anintegrated process for preparing ADN. A first process step includeshydrocyanating BD to produce 3PN over at least one zero-valent nickelcatalyst. A second process step of the integrated process involveshydrocyanating 3PN to produce ADN over at least one zero-valent nickelcatalyst and at least one Lewis acid. In this integrated process, atleast one of the zero-valent nickel catalysts used in one of the processsteps is transferred into the other process step.

In order to optimize the use of catalyst, recycle of catalyst isdesirable. However, undesirable substances, such as catalyst degradationproducts and reaction byproducts, may end up in catalyst recycle loopsalong with catalyst. When such catalyst degradation products andreaction byproducts are recycled along with catalysts, they tend tobuild up and cause loss of product yield and purity. Accordingly, thereis a need to recycle catalysts, while retaining optimal product yieldand purity. There is also a need to replenish catalyst which has beenlost by degradation.

SUMMARY OF THE INVENTION

Buildup of catalyst degradation products and reaction byproducts isreduced by a particular way of purifying a catalyst used forhydrocyanating 1,3-butadiene in a process for making adiponitrile. Thecatalyst is purified in a liquid/liquid extraction treatment andrecycled. Catalyst which has been lost by degradation is replenishedafter the extraction treatment.

Pentenenitrile is made in a process comprising two steps. In the firststep [i.e. step (a)], 1,3-butadiene is reacted with hydrogen cyanide ina first reaction zone (Z₁) in the presence of a first catalystcomprising zero-valent nickel (Ni^(o)) and a first phosphorus-containingligand to produce a reactor effluent comprising 3-pentenenitrile (3PN)and 2-methyl-3-butenenitrile (2M3BN). In the second step [i.e. step(b)], at least a portion of the 2M3BN made in the first step isisomerized in a second reaction zone (Z₂) in the presence of a secondcatalyst comprising zero-valent nickel (Ni^(o)) and a secondphosphorus-containing ligand to produce a reaction product comprising3PN.

An effluent stream comprising 3PN may be recovered from the secondreaction zone (Z₂). 3PN may also be recovered by distillation of thereaction product from the first reaction zone (Z₁). The recovered 3PNmay be contacted with HCN in a third reaction step [i.e. step (c)] in athird reaction zone (Z₃) in the presence of a third catalyst, comprisingzero-valent nickel (Ni^(o)) and a third phosphorus-containing ligand.The reaction in the third reaction zone (Z₃) takes place in the presenceof Lewis acid promoter.

Catalyst introduced into a reaction zone flows into, through and out ofthe reaction zone along with reactants and products. Any Lewis acidpromoter introduced into a reaction zone also flows through the reactionzone along with the flow of reactants, products and catalyst. Thecatalyst which flows through the first reaction zone is also referred toherein as the first catalyst. This first catalyst comprises zero valentnickel and a first phosphorus-containing ligand. The catalyst whichflows through the second reaction zone is also referred to herein as thesecond catalyst. This second catalyst comprises zero valent nickel and asecond phosphorus-containing ligand.

The first reaction zone is substantially free of Lewis acid promoter.The flow of recycled catalyst is controlled to avoid the introduction ofLewis acid promoter, which flows through the third reaction zone (Z₃),into the first reaction zone (Z₁).

In addition to 3-pentenenitrile (3PN) and 2-methyl-3-butenenitrile(2M3BN), the reaction product of step (a) further comprises dinitriles.These dinitriles comprise adiponitrile (ADN) and methylglutaronitrile(MGN). Adiponitrile (ADN) may be formed by the reaction of3-pentenenitrile (3PN) with HCN. Methylglutaronitrile (MGN) may beformed by the reaction of 2-methyl-3-butenenitrile (2M3BN) with HCN.

The formation of MGN in the first reaction zone (Z₁) is especiallyproblematic in that 2M3BN is converted before it can be recovered andisomerized into 3PN. In a process where 3PN is recovered and reactedwith HCN to form ADN, the production of one mole of MGN in the firstreaction zone (Z₁) results in a loss of two moles of HCN and one mole ofBD, which could otherwise be converted to ADN. Accordingly, unwantedproduction of MGN in the first reaction zone (Z₁) results in unwantedreduction of ADN yield, based on moles of HCN and BD reacted.

As catalyst flows through the first and second reaction zones, the zerovalent nickel content of the catalyst may be reduced and catalystdegradation byproducts may be produced. These catalyst degradationbyproducts comprise oxidized forms of nickel, oxidized forms of ligandand hydrolyzed forms of ligand.

At least a portion of the catalyst flowing from the first reaction zonealong with products or at least a portion of the catalyst flowing fromthe second reaction zone along with products or at least a portion ofthe catalyst flowing from both of the first and second reaction zonesalong with products is concentrated and recycled to the first reactionzone or the second reaction zone or both the first and second reactionzones. Concentration of catalyst flowing from the first reaction zonemay take place in one or more distillation steps. Similarly,concentration of the catalyst flowing from or the second reaction zonemay take place in one or more distillation steps.

In one embodiment, at least a portion of the catalyst flowing from thefirst reaction zone along with products is concentrated and recycled tothe first reaction zone. In another embodiment, at least a portion ofthe catalyst flowing from the second reaction zone along with productsis concentrated and recycled to the first reaction zone. In anotherembodiment, at least a portion of the catalyst flowing from both of thefirst and second reaction zones along with products is concentrated andrecycled to the first reaction zone. In another embodiment, at least aportion of the catalyst flowing from the first reaction zone along withproducts is concentrated and recycled to the second reaction zone. Inanother embodiment, at least a portion of the catalyst flowing from thesecond reaction zone along with products is concentrated and recycled tothe second reaction zone. In another embodiment, at least a portion ofthe catalyst flowing from both of the first and second reaction zonesalong with products is concentrated and recycled to the first reactionzone. In another embodiment, at least a portion of the catalyst flowingfrom both of the first and second reaction zones along with products isconcentrated and recycled to both the first and second reaction zones.

Catalyst is especially concentrated in column bottoms of columns used toconcentrate catalyst. Dinitriles produced in the first reaction zone(Z₁) or recycled into this first reaction zone (Z₁) also becomeconcentrated in column bottoms of columns used to concentrate catalyst.Catalysts tend to be less thermally stable in solutions with highconcentrations of these dinitriles, as opposed to catalyst solutionswith high concentrations of mononitriles, such as 3PN and 2M3BN. Whenthe production or build-up of dinitriles is excessively high,nickel/ligand complex of the catalyst may lack thermal stability and maybreak down releasing free ligand and non-complexed nickel in columnbottoms, where the nickel/ligand complex is exposed to the highesttemperatures. Nickel which is not complexed to ligand becomes insolubleand may plate out on high temperature surfaces such as exchange tubesand column walls, which, in turn, creates a host of problems includingloss of active catalyst and loss of throughput capacity, ultimatelyrequiring shut down of production.

At least two, and, optionally, three separate liquid/liquid extractionsteps are used to purify or regenerate catalysts. At least a portion ofthe concentrated catalyst from the first reaction zone is purified byremoving catalyst degradation byproducts and reaction byproducts in afirst liquid/liquid extraction step. A separate liquid/liquid extractionstep is used to treat the product from the third reaction zone. Purifiedcatalyst from the first liquid/liquid extraction step is recycled to thefirst reaction zone. Optionally, when the first catalyst and the secondcatalyst are the same, a portion of this purified catalyst may berecycled to the second reaction zone. Optionally, three separateliquid/liquid extraction sections are used for each catalyst. As usedherein, the terms “extraction section” and “extraction zone” refer tothe equipment and process steps for metering, charging, mixing, holding,separating and recycling components of a liquid-liquid extractionprocess. According to the option of using three separate extractionsections or zones, a portion of the first catalyst is extracted in afirst liquid/liquid extraction zone, a portion of the second catalyst isextracted in a second liquid/liquid extraction zone, and at least aportion, for example, all, of the third catalyst is extracted in a thirdliquid/liquid extraction zone. These three zones have dedicatedequipment for extraction, and equipment in different zones is notshared.

The first liquid/liquid extraction step comprises introducing a portionof the catalyst recycle stream, a first extraction solvent stream and adinitrile recycle stream comprising adiponitrile (ADN) into a firstliquid/liquid extraction zone. The first liquid/liquid extraction stepfurther comprises separating the liquids in the first liquid/liquidextraction zone into a first solvent phase and a first raffinate phase.The first solvent phase comprises extraction solvent and catalyst. Thefirst raffinate phase comprises adiponitrile (ADN), methylglutaronitrile(MGN), compounds with a higher boiling point than adiponitrile (ADN) andcompounds with a lower boiling point than methylglutaronitrile (MGN).

Catalyst from the first solvent phase obtained in the firstliquid/liquid extraction step is recycled to the first reaction zone.Optionally, when the first and second phosphorus-containing ligands arethe same, a portion of this purified catalyst may be recycled to thesecond reaction zone.

The first raffinate phase may be distilled in one or more distillationsteps to separate adiponitrile (ADN) and methylglutaronitrile (MGN) fromcompounds with a higher boiling point than adiponitrile (ADN) andcompounds with a lower boiling point than methylglutaronitrile (MGN) toobtain a first refined dinitrile stream. The first refined dinitrilestream may be further distilled to remove methylglutaronitrile (MGN)from the first refined dinitrile stream to obtain a second refineddinitrile stream enriched in adiponitrile. At least a portion of thesecond refined dinitrile stream is recycled to the first liquid/liquidextraction step as a dinitrile recycle stream.

The third catalyst is not contacted with the first extraction solvent inthe first liquid/liquid extraction step used to purify the firstcatalyst.

The presence of Lewis acid promoter in the third reaction zone (Z₃)promotes the reaction of 3-pentenenitrile (3PN) with HCN to produceadiponitrile (ADN). However, the presence of Lewis acid promoter in thefirst reaction zone (Z₁) promotes both the reaction of 3-pentenenitrile(3PN) with HCN to produce adiponitrile (ADN) and the reaction of2-methyl-3-butenenitrile with HCN to produce methylglutaronitrile (MGN).In the event that Lewis acid is introduced into the first reaction zone(Z₁), the amount of Lewis acid promoter in the first reaction zone (Z₁)should be less than the amount sufficient to increase the production ofMGN by no more than 10%, for example, no more than 5%, over theproduction of MGN in the absence of the Lewis acid promoter. The ratioof atomic equivalents of Ni to moles of Lewis acid in the first reactionzone may be less than 10:1 during normal process operation, for exampleat least 50% of the time, for example, at least 95% of the production of3-pentenenitrile.

The Lewis acid promoter in the third reaction zone (Z₃) has a higherboiling point than adiponitrile. The reaction product, third catalystand Lewis acid promoter flowing through the third reaction zone (Z₃) instep (c) may be contacted with an extraction solvent in an extractionzone to produce a solvent phase comprising the third catalyst and araffinate phase comprising adiponitrile product from step (c). Theraffinate phase also comprises compounds which are not adiponitrile,such as (1) compounds with a higher boiling point than adiponitrile and(2) compounds with a lower boiling point than adiponitrile. Theraffinate phase may be distilled in one or more distillation steps torecover a purified adiponitrile product stream and to remove compoundswhich are not adiponitrile from the raffinate phase. For example, mostof the Lewis acid promoter tends to partition into the raffinate phase,although at least a small amount of the promoter may also partition intothe solvent phase. The partitioning of compounds between the two phasesis discussed in U.S. Pat. No. 3,773,809. All of the Lewis acid promoterin the raffinate phase may be removed in distillation steps used torecover the adiponitrile product. The recovered adiponitrile product maybe used to provide dinitrile to the extraction zone for the firstcatalyst as may be needed to promote separation. The extraction zoneused to regenerate the first catalyst is different from the extractionzone used to regenerate the third catalyst. The compositions of theextraction solvents in these extraction zones may be the same ordifferent. The raffinate phases from these zones may be distilled in thesame or different distillation apparatus.

Zero valent nickel may be added to the purified first catalyst from theliquid/liquid extraction step after the catalyst is purified in thefirst liquid/liquid extraction step and before the purified firstcatalyst is recycled. For the purposes of the present disclosure, itwill be understood that a catalyst which flows through a reaction zoneis recycled when it is passed into the same or different reaction zone.Purified catalyst may be treated to increase its nickel content astaught in U.S. Pat. No. 4,416,825 to Ostermaier. Make-up ligand may alsobe added as needed, for example, following the catalyst purificationsteps.

In one embodiment, all of the zero valent nickel, which is added to makeup for zero-valent nickel lost by catalyst degradation or unwantedremoval during processing steps, may be added to the purified firstcatalyst after the catalyst has passed through the first liquid/liquidextraction zone.

At least a portion of the concentrated first catalyst may be recycleddirectly to the first reaction zone without being purified in aliquid/liquid extraction step. In such an embodiment, a purge stream maybe taken from a catalyst stream which is recycled. The purge stream maybe directed to the first liquid/liquid extraction step, where catalystis purified or regenerated.

When the ligands of the first and second catalysts are the same, andwhen the first and second catalysts both flow through the first andsecond reaction zone, the first and second catalyst may be recycled tothe first reaction zone or the second reaction zone or both the firstand second reaction zone, but not to the third reaction zone. The thirdcatalyst may be recycled to the third reaction zone, but not to thefirst reaction zone. In some embodiments, the third catalyst may berecycled to the second reaction zone, but not to the first reactionzone.

Examples of Lewis acid promoters used in the third reaction zone includezinc chloride and triphenylboron.

The first phosphorus-containing ligand of the first catalyst which flowsthrough the first reaction zone (Z₁) may be, for example, a monodentatephosphorus-containing ligand. The second phosphorus-containing ligand ofthe second catalyst which flows through the second reaction zone (Z₂)may be, for example, a monodentate or bidentate phosphorus-containingligand. The third phosphorus-containing ligand of the third catalystwhich flows through the third reaction zone (Z₃) for reacting 3PN withHCN may be, for example, a bidentate phosphorus-containing ligand. Thefirst phosphorus-containing ligand and the second phosphorus-containingligand may be the same or different. The second phosphorus-containingligand and the third phosphorus-containing ligand may be the same ordifferent. Examples of the first phosphorus-containing ligands aremondentate ligands of the formulaP(OR²)(OR³)(OR⁴)  (I)where R², R³ and R⁴ are the same or different and are aryl groups, forexample, phenyl and tolyl groups, where the aryl or phenyl groups areeach optionally substituted with up to four alkyl groups, each alkylgroup having from 1-4 carbon atoms. Particular examples of the firstphosphorus-containing ligand are tris(tolyl)phosphite (TTP) and amodified form of TTP, referred to herein as “MTTP.” In MTTP, at leastone of the tolyl groups in TTP is replaced with a phenyl group. TTP maybe prepared by reacting PCl₃ with one or more cresol isomers, which aresources of tolyl groups in the end product. MTTP may be prepared byreacting PCl₃ with a mixture of phenol, which a source of phenyl groupsin the end product, and one or more cresol isomers. Both TTP and MTTPtypically comprise a mixture of compounds.

Adiponitrile can be used in the manufacture of precursors useful in thesynthesis of nylon-6,6. For example, adiponitrile can be converted tohexamethylene diamine which can be used in the manufacture of nylon-6,6.In accordance with the invention, there is provided a process for themanufacture of hexamethylene diamine comprising a process of makingadiponitrile as described herein, followed by hydrogenation of theadiponitrile thus obtained to give hexamethylene diamine. There is alsoprovided a process for the manufacture of nylon-6,6 comprising a processof making adiponitrile as described herein, followed by hydrogenation ofthe adiponitrile thus obtained to give hexamethylene diamine, followedby reaction of the hexamethylene diamine with adipic acid, to givenylon-6,6.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of an integrated process for manufacturing3-pentenenitrile comprising the steps of hydrocyanating 1,3-butadiene,isomerizing 2-methyl-3-pentenenitrile and hydrocyanating3-pentenenitrile.

FIG. 2 is a representation of an example of separation section 1000 orseparation section 2000 shown in FIG. 1.

FIG. 3 is a representation of an example of adiponitrile purificationsection 3000 shown in FIG. 1.

FIG. 4 is a representation of an example of separation section 125 shownin FIG. 1.

FIG. 5 is a representation of an example of separation section 225 shownin FIG. 1.

FIG. 6 is a representation of a distillation apparatus which may be usedto separate pentenenitriles, catalyst and reaction byproducts from theeffluent of a first reaction zone (Z₁), where 1,3-butadiene is reactedwith hydrogen cyanide.

DETAILED DESCRIPTION OF THE INVENTION

Although the following detailed description contains many specifics forthe purpose of illustration, a person of ordinary skill in the art willappreciate that many variations and alterations to the following detailsare within the scope of the herein disclosed embodiments.

Accordingly, the following embodiments are set forth without any loss ofgenerality to, and without imposing limitations upon any claimedinvention. Before the present disclosure is described in greater detail,it is to be understood that this disclosure is not limited to particularembodiments described, as such may vary. It is also to be understoodthat the terminology used herein is for the purpose of describingparticular embodiments only, and is not intended to be limiting, sincethe scope of the present disclosure will be limited only by the appendedclaims.

Certain abbreviations and definitions used herein include the following:

-   -   ADN=adiponitrile; BD=1,3-butadiene; c2PN=cis-2-pentenenitrile;        c3PN=cis-3-pentenenitrile; C₈H₁₃C≡N=diolefinic acyclic and        monoolefinic cyclic mononitrile compounds of the chemical        formula C₈H₁₃C≡N; C₈H₁₄(C≡N)₂=monoolefinic acyclic and aliphatic        cyclic dinitrile compounds of the chemical formula C₈H₁₄(C≡N)₂;        dinitrile or dinitriles=ADN, MGN, and ESN unless specifically        limited; ESN=ethylsuccinonitrile; HC≡N or HCN=hydrogen cyanide        (i.e. hydrocyanic acid); 2M2BN=2-methyl-2-butenenitrile        including both (E)-2M2BN and (Z)-2M2BN isomers unless        specifically limited; 2M3BN=2-methyl-3-butenenitrile;        (E)-2M2BN=(E)-2-methyl-2-butenenitrile;        (Z)-2M2BN=(Z)-2-methyl-2-butenenitrile;        MGN=2-methylglutaronitrile; organic mononitrile=an organic        compound comprising a single nitrile group, for example, a        pentenenitrile; organic dinitrile=an organic compound comprising        two nitrile groups, for example, ADN; pentenenitrile or        pentenenitriles=4PN, 3PN, 2PN, 2M3BN, and 2M2BN isomers unless        specifically limited; 2PN=2-pentenenitrile including both c2PN        and t2PN isomers unless specifically limited;        3PN=3-pentenenitrile including both c3PN and t3PN unless        specifically limited; 4PN=4-pentenenitrile; ppm=parts per        million by weight unless stated otherwise;        t2PN=trans-2-pentenenitrile; t3PN=trans-3-pentenenitrile;        VN=valeronitrile.

As used herein a boiling point (BP) of a compound refers to thetemperature at which a pure form of the compound boils at atmosphericpressure. A listed boiling point is the temperature of a boiling pointfor a compound listed in at least one reliable source from the chemicalliterature.

As used herein, the terms “distillation apparatus” and “distillationcolumn” are used interchangeably, and both of these terms generallyrefer to equipment for performing distillation steps. For the purposesof this disclosure, a flasher is considered to be a distillation column.

Processes for making nitriles, such as 3PN and ADN, are describedherein. In one embodiment, 3PN is recovered as an end product. Inanother embodiment, 3PN is used as a feed in an integrated process tomake ADN.

A process for making 3PN, for example, in a first stage of an integratedprocesses for manufacturing adiponitrile (ADN), may involve reacting1,3-butadiene (BD) and hydrogen cyanide (HC≡N) in a first reaction zone(Z₁) in the presence of a first catalyst. The reaction may take placeunder sufficient reaction conditions to produce a reaction productcomprising 3-pentenenitrile (3PN) and 2-methyl-3-butenenitrile (2M3BN).The 2M3BN may be isomerized in a second reaction zone (Z₂) in thepresence of a second catalyst under sufficient isomerization conditionsto produce a reaction product comprising 3PN. The 3PN may be recoveredfrom the effluents of both the first reaction zone (Z₁) and the secondreaction zone (Z₂). In the second stage of an integrated process, therecovered 3PN may be reacted with HC≡N in a third reaction zone (Z₃) inthe presence of a third catalyst. The second stage reaction may takeplace under sufficient reaction conditions to produce a reaction productcomprising ADN. The ADN may be recovered. An integrated process does notrequire co-locality of the first and second stages.

The same catalyst may be used in all three reaction zones. Using thesame catalyst in all three reaction zones may lower capital andoperating costs. However, the transfer or sharing of a single catalystamong all three reaction zones (Z₁, Z₂ and Z₃) has disadvantages in thatsuch a process may be performance limited by a single catalyst in anyone or all 3 reaction zones. The physical properties of the singlecatalyst during required separation steps may also create disadvantages.For example, reboiler temperatures at certain points in the productseparation train may degrade less thermally stable catalysts. By meansof selecting catalysts for the individual reaction zones and limitingthe transfer of catalyst between reaction zones and/or stages, higher3PN and ADN product quality and chemical yields from BD and HC≡N may beachieved.

Selecting catalysts for individual reaction steps and limiting thetransfer of catalyst between reaction steps facilitates control ofreaction byproduct formation. Such byproducts include at least:4-vinyl-1-cyclohexene, 2-methyl-2-butenenitrile, and mononitrilecompounds of the chemical formula C₈H₁₃C≡N. As disclosed herein,separately treating the catalyst components and not co-mingling themamong process stages provides opportunities to manage the flow ofreaction byproducts, once formed, from one process step into anotherprocess step. For example, transfer of reaction byproducts in catalyststreams from the first process stage (e.g., in Z₁ and Z₂) to produce 3PNinto the second process stage to produce ADN (performed in Z₃) and viceversa, may be controlled.

Overview of FIG. 1

A more detailed description of a representative process for themanufacture of adiponitrile is made with reference to FIG. 1, whichprovides a simplified schematic representation of such a process. FIG. 1shows a first reaction zone (Z₁), where a mixture comprising1,3-butadiene and hydrogen cyanide is contacted in the presence of afirst catalyst, for example, comprising zero-valent Ni and a firstphosphorus-containing ligand, collectively a first catalyst system, toproduce a reaction product substantially comprising 3-pentenenitrile(3PN) and 2-methyl-3-butenenitrile (2M3BN).

As shown in FIG. 1, 1,3-butadiene reactant is fed into the firstreaction zone (Z₁) through line 100, hydrogen cyanide reactant is fedinto the first reaction zone (Z₁) through line 120, and catalyst is fedinto the first reaction zone (Z₁) through line 140. A reaction productstream is taken from the first reaction zone (Z₁) through line 122. Thereaction product stream in line 122 comprises products, byproducts,unreacted reactants and catalyst, which flows through the first reactionzone (Z₁). The reaction product stream 122 is introduced into aseparation section 125, to obtain, inter alia, a concentrated catalyststream 140 and product stream 200 comprising 2-methyl-3-butenenitrile(2M3BN). The separation section 125 may comprise one or moredistillation columns. An example of separation section 125 is shown inFIG. 4. Unreacted hydrogen cyanide and 1,3-butadiene may also beseparated from reaction products and catalyst in separation section 125.Unreacted 1,3-butadiene may be recycled to the first reaction zone (Z₁)through lines not shown in FIG. 1. A stream comprising 3-pentenenitrile(3PN) may also be withdrawn from separation section 125 through a linenot shown in FIG. 1. At least a portion of the catalyst separated fromreaction products in separation section 125 may be recycled to the firstreaction zone (Z₁) through line 140.

Subsequent to the reaction in the first reaction zone (Z₁), thesubstantial isomerization of 2M3BN in a second reaction zone (Z₂) isconducted in the presence of an isomerization catalyst to produce areaction product comprising substantially 3PN. The isomerizationcatalyst is also referred to herein as the second catalyst. Theisomerization catalyst may be the same as the catalyst introduced intothe first reaction zone (Z₁). Optionally, the isomerization catalyst maybe different from the catalyst introduced into the first reaction zone(Z₁).

As shown in FIG. 1, a feed comprising 2M3BN is introduced into thesecond reaction zone (Z₂) through line 200. Catalyst is introduced intothe second reaction zone (Z₂) through line 240. The effluent stream 222from the second reaction zone (Z₂) comprises catalyst and 3PN product.This effluent stream 222 passes into separation section 225 to obtain,inter alia, a 3PN product stream 300 and a concentrated catalyst stream240. Separation section 225 may comprise one or more distillationapparatus. FIG. 5 shows an example of such a separation section 225.

Catalyst recycle systems are shown in FIG. 1 for supplying catalyst tothe first reaction zone (Z₁) and the second reaction zone (Z₂). Thesecatalyst recycle systems comprise further systems for purifying at leasta portion of the catalyst prior to recycle.

In the catalyst recycle system for supplying catalyst to the firstreaction zone (Z₁), a portion of the concentrated catalyst stream inline 140 is diverted into catalyst purge stream 126.

Catalyst in purge stream 126 is in the form of a solution includingimpurities, such as reaction byproducts and catalyst degradationbyproducts. Catalyst in purge stream 126 is fed to liquid/liquidextraction zone 150 to at least partially purify or regenerate thecatalyst. The catalyst is purified or regenerated in that at least somebyproducts are removed from the catalyst solution.

A non-polar solvent, such as an alkane, is fed into the liquid/liquidextraction zone 150 through line 130. A polar solvent, which isimmiscible with the non-polar solvent, is also fed into theliquid/liquid extraction zone 150 through line 500.

In one embodiment, catalyst purge stream 126 and the polar solvent inline 500 are mixed prior to charging the combined stream to extractionzone 150. Although FIG. 1 schematically shows purge stream 126 andrecycle stream 500 separately added to extraction zone 150, it is to beunderstood that catalyst purge stream 126 and the polar solvent in line500 are preferably mixed before charging a combined stream to extractionzone 150.

In extraction zone 150, there is formed a non-polar phase comprisingnon-polar solvent and catalyst and a polar phase (e.g., a raffinate)comprising polar solvent and, for example, reaction byproducts andcatalyst degradation products. The non-polar phase is taken fromextraction zone 150 via line 134 to distillation apparatus 155. Thepolar phase is taken from extraction zone 150 via line 510 to separationsection 1000.

An example of separation section 1000 is described in greater detail inFIG. 2. Separation section 1000 may include, collectively, a series ofcolumns (K₁, K₂, K₃ and K₄) which provide for the removal of certainreaction byproducts and certain catalyst degradation products from thepolar solvent. The column bottom of K₄ provides polar solvent, which isreturned to extraction zone 150, via line 500.

Non-polar solvent is distillatively recovered in distillation apparatus155 and returned to extraction zone 150, via line 130. Extraction zone150, line 134, distillation apparatus 155 and line 130, collectively,form a recovery loop for recycling non-polar solvent into extractionzone 150. Extraction zone 150, line 510, separation section 1000 andline 500, collectively, form a recovery loop for recycling polar solventinto extraction zone 150. Additional non-polar solvent and polar solventmay be introduced into extraction zone 150 by lines not shown in FIG. 1.This additional solvent may be added for start up and for make-up ofsolvent lost during the course of the liquid/liquid extraction step.

Column bottoms from distillation column 155 include partially purifiedcatalyst. This catalyst is partially purified or regenerated in thesense that at least some of the catalyst degradation products and/orreaction byproducts have been separated from the solution containing thecatalyst. This partially purified catalyst may be taken fromdistillation column 155 through line 156 and introduced at any point forrecycle into the first reaction zone (Z₁). In FIG. 1, partially purifiedcatalyst may be taken from distillation column 155 through line 156 andtransferred into line 146 for introduction into catalyst recycle line140 for recycle into the first reaction zone (Z₁). FIG. 1 shows theintroduction of stream 146 downstream of the take-off stream 126, butthis stream may, optionally, be introduced upstream of the take-offstream 126. Stream 146 may also, optionally, be added to anycatalyst-containing stream associated with the first reaction zone (Z₁).Optionally, at least a portion of the partially purified catalyst streamin line 156 may be recycled into the second reaction zone (Z₂). In FIG.1, partially purified catalyst stream in line 156 may be transferredinto line 246 for introduction into catalyst recycle line 240 forrecycle into the second reaction zone (Z₂). However, it will beunderstood that other routes, not shown in FIG. 1, may be used forrouting partially purified first catalyst into the second reaction zone(Z₂).

The partially purified stream of first catalyst, which is subsequentlyreturned to the first reaction zone (Z₁) or, optionally, to the secondreaction zone (Z₂), may be provided with additional zero-valent Niand/or additional phosphorus-containing ligand. In FIG. 1, additionalzero-valent Ni and/or additional phosphorus-containing ligand may beprovided via line 145. Also as shown in FIG. 1, partially purifiedstream of first catalyst, which is subsequently fed to the secondreaction zone (Z₂), may be provided with additional zero-valent Niand/or phosphorus-containing ligand via line 245. However, it will beunderstood, that make-up catalyst may be added via different routes, notshown in FIG. 1. For example, make-up catalyst stream 145 may be chargedto other sections of the first reaction zone catalyst loop or, forexample, directly to the first reaction zone (Z₁).

In a particular embodiment shown in FIG. 1, the second reaction zone(Z₂) is provided with a second catalyst recovery system for supplyingcatalyst to the second reaction zone (Z₂). In this second catalystrecycle system, a portion of the concentrated catalyst stream in line240 is diverted into catalyst purge stream 226. This catalyst purgestream 226 is fed into liquid/liquid extraction zone 250. A non-polarsolvent, such as an alkane, is fed into the liquid/liquid extractionzone 250 through line 230. A polar solvent, which is immiscible with thenon-polar solvent, is also fed into the liquid/liquid extraction zone250 through line 700. Dinitriles from sources not shown in FIG. 1 may beadded to extraction zone 250, as needed to accomplish desired phaseseparation and extraction.

In one embodiment, catalyst purge stream 226 and the polar solvent inline 700 are mixed prior to charging the combined stream to extractionzone 250. Although FIG. 1 schematically shows purge stream 226 andrecycle stream 700 separately added to extraction zone 250, it is to beunderstood that catalyst purge stream 226 and the polar solvent in line700 are preferably mixed before charging a combined stream to extractionzone 250.

In one embodiment, a portion of the refined dinitrile product streamfrom the third reaction zone (Z₃) may be used as a feed to extractionzone 250. For example, a side stream (not shown) may be taken from line500 and introduced into extraction zone 250. In extraction zone 250,there is formed a non-polar phase comprising non-polar solvent andcatalyst and a polar phase (e.g., a raffinate) comprising, for example,polar solvent, reaction byproducts and certain catalyst degradationproducts. The non-polar phase is taken from extraction zone 250 via line234 to distillation apparatus 255. The polar phase is taken fromextraction zone 250 via line 710 to separation section 2000. Separationsection 2000 is described in greater detail in FIG. 2.

Separation section 2000 includes, collectively, a series of columns (K₁,K₂, K₃ and K₄) which provide for the separation of certain reactionby-products and catalyst degradation products. The column bottom of K₄provides polar solvent, which is returned to extraction zone 250, vialine 700. Additional polar solvent, in the form of adiponitrile, as needfor phase separation, may be provided from adiponitrile produced in thethird reaction zone (Z₃) through lines not shown in FIG. 1.

Non-polar solvent is distillatively recovered in distillation apparatus255 and returned to extraction zone 250, via line 230. Extraction zone250, line 234, distillation column 255 and line 230, collectively, forma recovery loop for recycling non-polar solvent into extraction zone250. Extraction zone 250, line 710, separation section 2000 and line700, collectively, form a recovery loop for recycling polar solvent intoextraction zone 250.

Column bottoms from distillation column 255 include partially purifiedcatalyst. This catalyst is partially purified or regenerated in thesense that at least some of the catalyst degradation products and/orreaction byproducts have been separated from the solution containing thecatalyst. This partially purified catalyst may be taken fromdistillation apparatus 255 through line 248 for introduction intocatalyst recycle line 240 for recycle into the second reaction zone(Z₂). Optionally, a side stream may be taken from line 248 into line247, and this side stream may be used as a catalyst feed to the firstreaction zone (Z₁), for example, by introducing the side stream fromline 247 into line 146 or line 140. Any partially purified stream ofcatalyst, which is subsequently fed to the second reaction zone (Z₂),may be provided with additional zero-valent Ni and/orphosphorus-containing ligand, for example, via line 245. Although notshown in FIG. 1, line 245 may optionally be fed directly into line 246or line 248 instead of line 240. Other ways of introducing make-upcatalyst are known in the art and may be used.

Although not shown in FIG. 1, it is possible that the first reactionzone (Z₁) and the second reaction zone (Z₂) share a single catalystrecovery system. A shared catalyst recovery system may be desirable whenthe first and second phosphorus-containing ligands are the same. In sucha shared system, the following features may be eliminated or shut down:lines 226, 230, 234, 247, 248, 700, and 710; extraction zone 250;distillation apparatus 255; and separation section 2000. Instead oftaking a purge stream via line 226, a purge stream may be taken via line227 and introduced into line 126 or directly into extraction zone 150.In such a shared catalyst recovery system, any partially purifiedcatalyst stream entering the second reaction zone (Z₂) would passthrough lines 246 and 240 according to the configuration shown in FIG.1.

The 3PN product in line 300 is introduced into the third reaction zone(Z₃), where 3PN is reacted with HCN. 3PN from separation section 125 mayalso be introduced into the third reaction zone (Z₃) through a line orlines not shown in FIG. 1. The HCN reactant feed is introduced into thethird reaction zone (Z₃) through line 220. A third catalyst comprising,for example, zero-valent Ni and a third phosphorus-containing ligand,collectively a third catalyst system, and a Lewis acid promoter isintroduced into the third reaction zone (Z₃) through line 340. Thereaction of 3PN and HCN in the third reaction zone (Z₃) produces areaction product containing adiponitrile. A reaction product stream istaken from the third reaction zone (Z₃) by line 400. The reactionproduct stream comprises, for example, adiponitrile, catalyst, promoter,and unreacted reactants. The reaction product stream may optionally bepassed through a separation section (not shown in FIG. 1) to removeunreacted reactants, prior to separation of catalyst from adiponitrileproduct.

Catalyst and adiponitrile product from the product stream in line 400are passed into liquid/liquid extraction zone 370. A non-polar solvent,such as an alkane, is fed into the liquid/liquid extraction zone 370through line 330. The non-polar solvent introduced into theliquid/liquid extraction zone 370 may have the same or differentcomposition as the non-polar solvent introduced into the liquid/liquidextraction zone 150. Together, non-polar solvent from line 330 andadiponitrile product from line 400 comprise an extractant system ofimmiscible components. In extraction zone 370, there is formed anon-polar phase comprising non-polar solvent and catalyst and a polarphase (e.g., a raffinate) comprising adiponitrile, promoter and catalystdegradation products.

The non-polar phase is taken from extraction zone 370 via line 334 todistillation apparatus 375. The polar phase comprising adiponitrile istaken from extraction zone 370 via line 600 to adiponitrile purificationsection 3000. Adiponitrile purification section 3000 is described ingreater detail in FIG. 3.

Adiponitrile purification section 3000 may include, collectively, aseries of columns (K′₁, K′₂, K′₃ and K′₄) which provide for theseparation of impurities, such as reaction byproducts and catalystdegradation products. The column bottom of K′₄ provides the purifiedadiponitrile product, which is recovered in line 660. A portion of thepurified adiponitrile product may optionally be returned to extractionzone 150 or extraction zone 250 (by lines not shown in FIG. 1) tofacilitate phase separation in these extraction zones.

Non-polar solvent is distillatively recovered in distillation apparatus375 and returned to extraction zone 370, via line 330. Extraction zone370, line 334, distillation apparatus 375 and line 330, collectively,form a recovery loop for recycling non-polar solvent into extractionzone 370. Column bottoms from distillation column 375 include partiallypurified catalyst. This partially purified catalyst may be taken fromdistillation column 375 through line 340 for recycle of catalyst intothe third reaction zone (Z₃). The partially purified stream of thirdcatalyst in line 340, which is subsequently returned to the thirdreaction zone (Z₃), may be provided with make-up quantities ofadditional zero-valent Ni and/or third phosphorus-containing ligandalong with promoter. In FIG. 1, make-up quantities of additionalzero-valent Ni and/or third phosphorus-containing ligand and/or promotermay be added via line 345. However, it will be appreciated that thereare other ways of introducing make-up catalyst and promoter. Forexample, all or a portion of the recycled catalyst stream 340 may becharged to a catalyst reactor to increase its nickel content and theeffluent from the catalyst reactor may introduced at a suitable point.

Overview of FIG. 2

FIG. 2 shows a distillation train, which may be used as separationsection 1000 or separation section 2000, shown in FIG. 1. In FIG. 2,line 515 represents either line 510 or line 710 of FIG. 1. Line 515transports a raffinate stream from either extraction zone 150 orextraction zone 250 into separation section 1000 or separation section2000, as shown in FIG. 1. The raffinate stream in line 515 is firstpassed into distillation column K₁, where extraction solvent isseparated from higher boiling components of the raffinate stream. Inparticular, extraction solvent, such as cyclohexane, is withdrawn fromdistillation column K₁ through line 525, and higher boiling componentsof the raffinate stream are withdrawn from distillation column K₁through line 520.

The solvent-depleted stream in line 520 is then passed into distillationcolumn K₂, where pentenenitrile is separated from higher boilingcomponents remaining in the raffinate stream. In particular,pentenenitrile, such as 3PN and any 2M3BN, present is withdrawn fromdistillation column K₂ through line 550, and higher boiling componentsof the raffinate stream are withdrawn from distillation column K₂through line 530.

The pentenenitrile-depleted stream in line 530 is then passed intodistillation column K₃, where dinitriles are separated from higherboiling components remaining in the raffinate stream. In particular,dinitriles, such as ADN and MGN, are withdrawn from distillation columnK₃ through line 535, and higher boiling components of the raffinatestream are withdrawn from distillation column K₃ through line 540. Thesehigher boiling components in line 540 may comprise, for example,catalyst degradation products.

The dinitrile-enriched stream in line 535 is then passed intodistillation column K₄, where adiponitrile is separated from lowerboiling dinitriles, such as MGN. In particular, MGN is withdrawn fromdistillation column K₄ through line 420. The MGN-containing stream inline 420 may also include C₈H₁₃C≡N compounds and phenolic compounds. Anadiponitrile-enriched stream is withdrawn from distillation column K₄through line 560. In FIG. 2, line 560 represents either line 500 or line700 of FIG. 1. As shown in FIG. 1, the adiponitrile-enriched stream inline 500 is recycled to the liquid/liquid extraction zone 150, and theadiponitrile-enriched stream in line 700 is recycled to theliquid/liquid extraction zone 250.

Overview of FIG. 3

FIG. 3 shows a distillation train, which may be used as adiponitrilepurification section 3000, shown in FIG. 1. Line 600 transports araffinate stream from extraction zone 370 into distillation column K′₁,where extraction solvent is separated from higher boiling components ofthe raffinate stream. In particular, extraction solvent, such ascyclohexane, is withdrawn from distillation column K′₁ through line 625,and higher boiling components of the raffinate stream are withdrawn fromdistillation column K′₁ through line 620.

The solvent-depleted stream in line 620 is then passed into distillationcolumn K′₂, where pentenenitrile is separated from higher boilingcomponents remaining in the raffinate stream. In particular,pentenenitrile, such as 3PN and any 2M3BN present, is withdrawn fromdistillation column K′₂ through line 650, and higher boiling componentsof the raffinate stream are withdrawn from distillation column K′₂through line 630.

The pentenenitrile-depleted stream in line 630 is then passed intodistillation column K′₃, where dinitriles are separated from higherboiling components remaining in the raffinate stream. In particular,dinitriles, such as ADN and MGN, are withdrawn from distillation columnK′₃ through line 635, and higher boiling components of the raffinatestream are withdrawn from distillation column K′₃ through line 640.These higher boiling components in line 640 may comprise, for example,catalyst degradation products.

The dinitrile-enriched stream in line 635 is then passed intodistillation column K′₄, where adiponitrile is separated from lowerboiling dinitriles, such as MGN. In particular, MGN is withdrawn fromdistillation column K′₄ through line 670, and a purified adiponitrilestream is withdrawn from distillation column K′₄ through line 660.

Overview of FIG. 4

FIG. 4 is a schematic representation of an example of a distillationtrain, which may be used as separation section 125, shown in FIG. 1.Stream 122 comprising 3PN, 2M3BN, at least one catalyst, and BD istransferred into an apparatus 810 for distillation. In this apparatus,stream 122 is distilled to obtain a BD-enriched stream 812 and aBD-depleted stream 813 comprising 3PN, 2M3BN, and at least one catalyst.The BD-enriched stream 812 may be recycled to the first reaction zone(Z₁).

The BD-depleted stream 813, which comprises 3PN, 2M3BN, and at least onecatalyst is then transferred to another apparatus 820 for furtherdistillation. In this apparatus, stream 813 is distilled to obtain a topproduct stream 824 enriched in BD, a stream 825, comprising 3PN and2M3BN, and a bottom product stream 140 enriched in at least onecatalyst. Stream 824 enriched in BD may also be recycled to the firstreaction zone (Z₁). If excess dinitriles are introduced into apparatus820, the catalyst may thermally degrade, causing nickel and ligand todisassociate and resulting in plating out of nickel on high-temperaturesurfaces such as exchanger tubes and reboiler wall surfaces or,alternatively, trigger precipitation of nickel solids, for example, inthe column bottoms.

Stream 825, comprising 3PN and 2M3BN, is transferred at least in part toanother distillation apparatus 830. In this apparatus, the distillationof stream 825 is distilled to obtain 2M3BN-enriched stream 200 and2M3BN-depleted stream 838 comprising 3PN. As described in the “NylonIntermediates Refining” section of the PhD thesis dissertation by DecioHeringer Coutinho, University of Texas at Dallas, December 2001, stream200 may be obtained at the top region of the distillation apparatus,while the stream 838 may be obtained at the bottom region of thedistillation apparatus.

FIG. 4 illustrates one distillation system for distilling the effluentfrom the first reaction zone (Z₁). However, it will be understood thatit is within the skill in the art to design and operate otherdistillation systems to achieve the same or essentially the sameresults. For example, depending upon the thermal stability of catalyst,it may be possible to combine distillation apparatus 810 anddistillation apparatus 820 into a single distillation apparatus, where aBN-enriched stream is withdraw as a top draw, a PN-enriched stream iswithdrawn as a side draw, and a catalyst-enriched stream is withdrawn asa bottom draw.

Overview of FIG. 5

FIG. 5 is a schematic representation of an example of a distillationtrain, which may be used as separation section 225, shown in FIG. 1. Theisomerization reaction effluent in stream 222 obtained in the secondreaction zone is distilled to recover catalyst and products. In adistillation step not shown in FIG. 5, light boilers may first beremoved from stream 222. Low boilers are compounds which boil attemperatures less than pentenenitriles. Examples of light boilersinclude, butane, butadiene and cyclohexane. Compounds in stream 222,which boil at the same temperature or higher than pentenenitrile, areintroduced into distillation apparatus 940. A pentenenitrile-enrichedstream 942, comprising 3PN, 2M3BN, and (Z)-2M2BN, may be obtained fromthe distillation apparatus 940. Stream 942 may also comprise otherpentenenitriles, selected from 4PN, (E)-2M2BN, or a combination thereof,and optionally dimerized BD compounds having the empirical formulaC₈H₁₂, such as VCH and ethylidene cyclohexene isomers. Apentenenitrile-depleted stream 240, enriched in at least one catalyst,may be obtained as the bottom product.

U.S. Pat. No. 3,852,329 describes a process for “reduced loss toundesirable products such as 2-methyl-2-butenenitrile.” An objective ofthe distillation of stream 942 is to purge at least a portion of thelower-boiling (Z)-2M2BN isomer from the 3PN and 2M3BN reaction productmixture.

Stream 942, comprising 3PN, 2M3BN, and (Z)-2M2BN, is distilled indistillation apparatus 950. Stream 954 is obtained as an overheadproduct that is enriched in (Z)-2M2BN. Stream 955, comprising 3PN and2M3BN, is obtained as a bottom product and is depleted in (Z)-2M2BN.“Enriched” and “depleted” in (Z)-2M2BN are relative to its concentrationin stream 942.

Stream 954 may also comprise other pentenenitriles, selected from thegroup comprising 2M3BN, (E)-2M2BN, and optionally dimerized BD compoundshaving the empirical formula C₈H₁₂, such as VCH and ethylidenecyclohexene isomers. Stream 955 may also comprise other pentenenitriles,selected from the group comprising 4PN, 2PN, and (E)-2M2BN.

In one embodiment, the distillation is operated in such a manner tocause dimerized BD compounds to be enriched in stream 954 and depletedin stream 955, both relative to the concentration of dimerized BDcompounds in stream 942. In another embodiment, dimerized BD compoundsare enriched in stream 954 through an azeotrope of said compounds with2M3BN. In another embodiment, stream 954 comprises greater than 1% byweight, for example greater than 5% by weight, for example greater than10% by weight of 2M3BN, relative to the total mass of stream 954.

Stream 955, comprising 3PN and 2M3BN, may be transferred at least inpart to distillation apparatus 960. In this apparatus, the distillationof stream 955 occurs to obtain 2M3BN-enriched stream 967 and a2M3BN-depleted stream 300 comprising 3PN. As described in the “NylonIntermediates Refining” section of the PhD thesis dissertation by DecioHeringer Coutinho, University of Texas at Dallas, December 2001, stream967 may be obtained at the top region of the distillation apparatus,while the stream 300 may be obtained at the bottom region of thedistillation apparatus.

FIG. 5 illustrates one distillation system for distilling the effluentfrom the second reaction zone (Z₂). However, it will be understood thatit is within the skill in the art to design and operate otherdistillation systems to achieve the same or essentially the sameresults. For example, a distillation step to remove low boilers may beinserted into the system, as described above. It is also possible toshare equipment used for distilling the effluent from the first reactionzone. For example, a stream comprising 3PN and 2M3BN obtained bydistilling the effluent from the second reaction zone (Z₂) may be passedto a distillation apparatus, such as distillation apparatus 830, used inthe distillation of the effluent form the from the first reaction zone(Z₁), to obtain a 3PN-enriched stream and a 2M3BN-enriched stream.

Overview of FIG. 6

FIG. 6 illustrates features of a distillation column having an upperdraw outlet, a bottom draw outlet and a side draw outlet. A streamenriched in pentenenitrile is withdrawn from the top draw outlet. Astream enriched in catalyst is withdrawn from the bottom draw outlet.This distillation column may be designed and operated to optimizecollection of liquids having boiling between 147 and 295° C., which arewithdrawn from the side draw outlet.

In FIG. 6, a feed is introduced into distillation column 850 throughstream 852. The feed in stream 852 comprises (1) pentenenitriles,including 3-pentenenitrile and 2-methyl-3-butenenitrile, (2)adiponitrile, (3) compounds having a boiling point between that of3-pentenenitrile and adiponitrile and (4) compounds having a boilingpoint higher than adiponitrile.

3-Pentenenitrile has a boiling point of 147° C. Other pentenenitrileshave a boiling point of less than 147° C. Adiponitrile has a boilingpoint of 295° C. Compounds which have a boiling point between 147 and295° C. are also referred to herein as “intermediate boilers.”Intermediate boilers which may be present in feed stream 852 compriseone or more compounds selected from the group consisting of phenol,cresols, C₈H₁₃C≡N compounds, methylglutaronitrile (MGN) andtertiary-butylcatechol (TBC).

Compounds in feed stream 852 having a higher boiling point thanadiponitrile include catalyst and catalyst degradation byproducts. Thefeed stream introduced into distillation column 850 through stream 852may be obtained by distilling the reaction effluent from the firstreaction zone (Z₁) under conditions sufficient to generate abutadiene-enriched stream and a butadiene-depleted stream. Thisbutadiene-depleted stream may be fed into distillation column 850through stream 852.

A rectifying section comprising at least one, for example, at least two,stages of separation is provided between the feed inlet and the upperdraw outlet. In FIG. 6, the position of the feed inlet is shown as theposition where stream 852 enters the distillation column 850. Also, theposition of the upper draw outlet is shown as the position where stream856 exits the distillation column 850. A packing section 854 is alsoprovided in distillation column 850 above the position where feed stream852 enters distillation column 850. Stream 856 is enriched inpentenenitriles relative to the concentration of pentenenitriles in feedstream 852.

Compounds are withdrawn from the bottom draw outlet of distillationcolumn 850 through stream 858. Stream 858 is enriched in catalystrelative to the concentration of catalyst in feed stream 852. Stream 858passes through pump 860 to stream 862. A portion of thecatalyst-containing stream 862 may be recycled to the first reactionzone (Z₁) and a portion of stream 862 may be withdrawn as a purgestream, which is subsequently purified, for example, in a liquid/liquidextraction zone. A portion of stream 862 is withdrawn as a side stream864, which is, in turn, heated in heat exchanger 866. The heated stream868 is then returned to a lower section of distillation column 868. Theloop comprising stream 858, pump 860, stream 862, side stream 864, heatexchanger 866, stream 868 and column bottoms constitutes a reboilersection for providing vapor which passes upwards through distillationcolumn 850. This vapor comprises pentenenitrile vapor and adiponitrilevapor.

Above this reboiler section and above the point of entry of feed fromstream 852, a liquid collection apparatus 870 is provided. This liquidcollection apparatus 870 may be a chimney tray. This liquid collectionapparatus 870 has at least one opening, which permits vapor ascendingupwards through the column to pass through the apparatus. However, theliquid collection apparatus 870 does not permit liquids descendingthrough the column to pass through. For example, the liquid collectionapparatus 870 may have a tray section for collecting liquids.Accordingly, liquids descending from a point above the liquid collectionapparatus 870 in the column are collected.

Liquids collected in liquid collection apparatus 870 are withdrawn fromthe distillation column through stream 872. This stream 872 passesthrough pump 874 to stream 876. A portion of the collected liquid instream 874 is withdrawn as side stream 878. A portion of the liquidcollected in stream 876 is heated in heat exchanger 880. The heatedstream 882 is then returned to distillation column at a point above theliquid collection apparatus 870. The loop comprising stream 872, pump874, stream 876, heat exchanger 880, stream 882 and liquid collectionapparatus 870 constitutes a reboiler section for heating the collectedliquids. This reboiler section is operated in a manner such that thepercentage of pentenenitriles in the collected liquid which is vaporizedis greater than the percentage of adiponitrile in the collected liquidwhich is vaporized. Heat supplied by heat exchanger 880 may besufficient to restore heat lost during the collection and recycle ofliquids through the reboiler loop, without supplying excess heat. Heatexchanger 880 may be considered to be a trim heater.

The pump around liquid return point from the reboiler for heatingcollected liquid from side draw stream 872 is shown in FIG. 6 as thepoint where stream 882 enters distillation column 850. The section ofthe distillation column above this pump around liquid return point maybe considered to be the pentenenitrile flasher section of column 850.This pentenenitrile flasher section may contain one or more stages ofseparation in the form of trays or packing. These stages of separationare illustrated by packing 854 in FIG. 6. The overhead stream from thepentenenitrile flasher is enriched in pentenenitriles and normallyrequires no condensation and reflux to the flasher.

The distillation column 850 may be operated in a manner such that thecatalyst-enriched stream withdrawn as stream 862 comprises at least 5%by weight of pentenenitrile including the sum of 3-pentenenitrile and2-methyl-3-butenenitrile. The distillation column 850 may further beoperated in a manner such that adiponitrile and intermediate boilers,including, for example, MGN, C₈H₁₃C≡N compounds, phenol and cresols, arecollected in the liquid collection apparatus 870. The collected liquidis withdrawn in stream 878. This stream 878 may be passed eitherdirectly or indirectly (e.g., into the catalyst purge stream) to anextraction zone. In this way, there is achieved an increased amount ofintermediate boilers passed into an extraction zone and separated fromrecycled catalyst. In another option, compounds in stream 878 may beseparated and recovered in a distillation process.

Low, Intermediate and High Boilers

When 1,3-butenenitrile is reacted with hydrogen cyanide, both3-pentenenitrile and 2-methyl-3-butenenitrile are produced.2-methyl-3-butenenitrile has a listed boiling point of 125° C.,cis-2-pentenenitrile has a listed boiling point of 127-128° C., andtrans-3-pentenenitrile has a listed boiling point of 144-147° C. In anintegrated process for making adiponitrile, 3-pentenenitrile is reactedwith hydrogen cyanide to produce adiponitrile. Adiponitrile has a listedboiling point of 295° C.

When 3-pentenenitrile and adiponitrile are produced by theabove-mentioned process, reaction byproducts and catalyst degradationbyproducts may also be produced. Unreacted reactants may also becomeentrained in the effluent from reaction zones used to producepentenenitriles and adiponitrile.

Certain compounds in effluents from reaction zones are referred toherein as low, intermediate or high boilers.

As used herein, the term “low boilers” refers to compounds having alower boiling point than the listed boiling point of2-methyl-3-butenenitrile, i.e. 125° C. Examples of such low boilersinclude 1-butene, 1,3 butadiene, trans-2-butene, hydrogen cyanide, andcyclohexane. 1-butene has a listed boiling point of −6.3° C.1,3-butadiene has a listed boiling point of −4.5° C. Trans-2-butene hasa listed boiling point of 1° C. Hydrogen cyanide has a listed boilingpoint of 25.7° C. Cyclohexane has a listed boiling point of 80.7° C.(Z)-2M2BN has a listed boiling point of 121.6° C.

Compounds having a boiling point between 147° C. and 295° C. arereferred to herein as intermediate boilers. The listed boiling point for3-pentenenitrile may be as high as 147° C. 295° C. is the listed boilingpoint for adiponitrile. Examples of compounds which are intermediateboilers include C₉ mononitriles, phenol, cresols, TBC, MGN and ESN. C₉mononitriles encompass a broad range of compounds having boiling pointsbetween 147 and 295° C. Phenol and cresols have listed boiling points ofbetween 180 and 210° C. Tertiary-butylcatechol (TBC) has a listedboiling point of 285° C. Methylglutaronitrile, especially2-methylglutaronitrile (MGN), has a listed boiling point of 269-271° C.2-Ethylsuccinonitrile (ESN) has a listed boiling point of 264° C.

High boilers have a listed boiling point above that of adiponitrile,i.e. 295° C. Examples of high boilers include TTP or MTTP, phosphoruscontaining ligand degradation products, Ni(CN)₂, ZnCl₂ andtriphenylboron.

Effluents from reaction zones, Z₁, Z₂ and Z₃, include low boilers,intermediate boilers and high boilers. Desired products, such as3-pentenenitrile and adiponitrile, need to be purified, in thatsolutions of these desired products need to be separated fromimpurities, which are low boilers, intermediate boilers and highboilers. Catalyst, which is to be recycled, also needs to be purified orregenerated by removing certain reaction byproducts and catalystdegradation byproducts from streams including solutions of catalyst.

Reaction byproducts produced in the first reaction zone (Z₁) includeC₈H₁₃C≡N compounds. These C₈H₁₃C≡N compounds may be produced bydimerization of 1,3-butadiene and hydrocyanation of such dimers.C₈H₁₃C≡N compounds may be separated from catalyst in the extraction zoneused to purify the catalyst from the first reaction zone (Z₁) or thesecond reaction zone (Z₂) or both the first reaction zone (Z₁) and thesecond reaction zone (Z₂). C₈H₁₃C≡N compounds generally have normalboiling points within the range of 150° C. to 295° C.

The reaction product from the first reaction zone (Z₁) may comprise oneor more phenolic compounds of the formula

where R¹ is H or an alkyl group having 1 to 4 carbon atoms, and n is 0to 4, provided that when the phenolic compound of formula (II) has morethan one alkyl group, these alkyl groups may be the same or different.Examples of such phenolic compounds include phenol and cresols. Inparticular, cresols are used to make TTP ligands, and both phenol andcresols are used to make MTTP ligands. Consequently, cresols may bepresent as impurities when the first phosphorus-containing ligand isTTP, and both phenol and cresols may be present as impurities when thefirst phosphorus-containing ligand is MTTP. Cresols may also be producedin the first reaction zone (Z₁) or at another point upstream of theextraction zone by unwanted hydrolysis of TTP ligands. Furthermore, bothphenol and cresols may also be produced in the first reaction zone (Z₁)or at another point upstream of the extraction zone by unwantedhydrolysis of MTTP ligands. The phenol and cresol impurities have anapproximate boiling point falling within the range of 180° C. to 210° C.By limiting the amount of phenolic compounds of formula (II) enteringinto the third reaction zone (Z₃), degradation of the third catalyst,particularly the third phosphorus-containing ligand, may be reduced.

In the distillation steps upstream of the extraction zone, compoundssuch as 3PN and 2M3BN, having boiling points less than, for example,150° C., are separated from a higher boiling, catalyst-containingstream. Since tertiary-butylcatechol, C₈H₁₃C≡N compounds, phenol andcresols have boiling points higher than 150° C., they may pass alongwith catalyst in the distillation train upstream of the extraction zone.However, when tertiary-butylcatechol, C₈H₁₃C≡N compounds, phenol andcresols are present, significant amounts if these compounds are taken upin the raffinate phase of the extraction zone. C₈H₁₃C≡N compounds,phenol and cresols in the raffinate phase may be separated fromdinitriles in the distillation train used to produce a dinitrile recyclestream to be passed into the extraction zone.

Catalyst Purification

Buildup of catalyst degradation products and reaction byproducts may bereduced by a particular way of purifying a catalyst used forhydrocyanating 1,3-butadiene in a process for making adiponitrile. Thecatalyst may be purified in a liquid/liquid extraction treatment. Inparticular, separate extraction zones may be used to purify the firstand third catalysts. In FIG. 1, these zones are represented byextraction zone 150 and extraction zone 370.

Addition of Make-Up Catalyst

During the course of the reaction in the first reaction zone (Z₁), aswell as in subsequent processing of the reactor effluent, for example,during distillation, a portion of the first catalyst may degraded orlost. There is a need to replenish catalyst which is degraded or lost.As shown in FIG. 1, catalyst which has been lost by degradation isreplenished after the extraction treatment. In FIG. 1, make-up catalystis added to catalyst recycle stream 146 through line 145 after thecatalyst passes through extraction zone 150. However, it will beunderstood that catalyst, which passes through extraction zone 150, maybe provided with make-up catalyst and reintroduced into reaction systemin different locations.

Removal of C₈H₁₃C≡N Compounds

Reaction byproducts produced during the reaction of 1,3-butadiene andHCN in a first reaction zone (Z₁) include C₈H₁₃C≡N compounds. TheseC₈H₁₃C≡N compounds may be produced by dimerization of 1,3-butadiene andhydrocyanation of such dimers. When such C₈H₁₃C≡N compounds areintroduced into a reaction zone for producing adiponitrile by thereaction of 3PN with HCN, these C₈H₁₃C≡N compounds may react with HCN toproduce unwanted C₈H₁₄(C≡N)₂ compounds. Methods for removing theseC₈H₁₃C≡N compounds are discussed below.

C₈H₁₃C≡N compounds are separated from a first catalyst in aliquid/liquid extraction zone. In FIG. 1, this separation takes place inextraction zone 150. C₈H₁₃C≡N compounds which enter into the raffinatestream may, in turn, be removed by distillation. In FIG. 2, C₈H₁₃C≡Ncompounds are removed from adiponitrile in column K₄ via stream 420.

A significant amount of the C₉ mononitriles in the raffinate streamentering separation sections 1000 and 2000, through lines 510 and 710,respectively, may pass into line 420, along with MGN.

C₉ mononitriles may not completely separate from pentenenitriles in adistillation step used to remove pentenenitriles from C₉ mononitriles.Accordingly, pentenenitriles removed from higher boiling components ofthe raffinate phase by distillation may contain some C₉ mononitriles.Pentenenitriles removed from higher boiling components of the raffinatephase may be treated to remove C₉ mononitriles. Pentenenitriles removedfrom higher boiling components of the raffinate phase may be used toprepare make-up catalyst for recycle into the first reaction zone (Z₁),the second reaction zone (Z₂) or both the first reaction zone (Z₁) andthe second reaction zone (Z₂).

The effluent from the first reaction zone of step (a) may be distilledin a single distillation column to provide a stream enriched in 2M3BNand a stream enriched in both 3-pentenenitrile and C₉ mononitriles. Thestream enriched in 3-pentenenitrile and C₉ mononitriles may be distilledto separate the 3-pentenenitrile from the C₉ mononitriles.

The effluent from the first reaction zone of step (a) may be distilledin a single distillation column to provide (i) a stream enriched in2M3BN, (ii) a stream enriched in 3-pentenenitrile and (iii) a streamenriched in C₉ mononitriles. The stream enriched in 2M3BN may be takenas a top draw, the stream enriched in 3-pentenenitrile may taken as aside draw, and the stream enriched in C₉ mononitriles may be taken as abottom draw.

In the context of this specification, a C₉ mononitrile is generallydefined as an aliphatic mononitrile compound comprising a total of ninecarbon atoms (C₉). A C₉ mononitrile with a carbon-carbon double bond iscapable of further reacting with hydrogen cyanide to produce a C₁₀dinitrile, such as C₈H₁₄(C≡N)₂. Without being limited by theory, it istheorized that C₉ mononitriles are various isomers of diolefinic acyclicC₉ mononitrile compounds with the chemical formula C₈H₁₃C≡N andmonoolefinic cyclic C₉ mononitrile compounds with the chemical formulaC₈H₁₃C≡N. Compounds with the chemical formula C₈H₁₃C≡N may arise bycombining two 1,3-butadiene molecules with one hydrogen cyanidemolecule.

Gas chromatographic (GC) methods to quantify the amounts of five carbonpentenenitrile isomers (produced from 1,3-butadiene hydrocyanation and2-methyl-3-butenenitrile isomerization) and six carbon dinitriles(produced from pentenenitrile hydrocyanation) in a process sample mayalso be used to quantify C₉ mononitrile compounds. Dependent upon the GCcolumn utilized, the C₉ mononitriles can appear as GC peaks withretention times between those peaks for 3-pentenenitrile andadiponitrile; an observation that is consistent with these C₉mononitriles possessing boiling points, at a given set of conditions,that are intermediate between the boiling point of 3-pentenenitrile andthe boiling point of adiponitrile at the same conditions. Using GC/massspectroscopy with electron impact ionization method, the observation ofone or more positive ions selected from the group consisting of m/e(mass/charge ratio)=135 [C₈H₁₃C≡N]+, 134 [C₈H₁₃C≡N minus H]+, 120[C₈H₁₃C≡N minus CH₃]+, 106 [C₈H₁₃C≡N minus C₂H₅]+, 95 [C₈H₁₃C≡N minusCH₂C≡N]+, 94 [C₈H₁₃C≡N minus C₃H₅]+, and 81 [C₈H₁₃C≡N minus C₂H₄C≡N]+can then be used to identify which of these peaks comprise a C₉mononitrile and thereby quantify the amounts of C₉ mononitriles in aprocess sample by GC analysis.

During 3-pentenenitrile hydrocyanation to produce adiponitrile in thepresence of nickel complexes of phosphorus-containing ligands and Lewisacid, GC analyses provide evidence that certain C₉ mononitrile compoundswith a carbon-carbon double bond may also be hydrocyanated to producealiphatic dinitrile compounds with a total of ten carbon atoms (C₁₀).Without being limited by theory, it is believed that these C₁₀dinitriles are various isomers of monoolefinic acyclic C₁₀ dinitrilecompounds with the chemical formula C₈H₁₄(C≡N)₂ and cyclic C₁₀ dinitrilecompounds with the chemical formula C₈₁H₁₄(C≡N)₂.

The C₁₀ dinitriles appear as GC peaks with retention times before andafter a retention time for 1,6-dicyanohexane [eight carbon dinitrile]utilized as a GC internal standard. Using GC/mass spectroscopy withelectron impact ionization method, the observation of one or morepositive ions selected from the group consisting of m/e (mass/chargeratio)=162 [C₈H₁₄(C≡N)₂]+, 161 [C₈H₁₄(C≡N)₂ minus H]+, 147 [C₈H₁₄(C≡N)₂minus CH₃]+, 135 [C₈H₁₄(C≡N)₂ minus C₂H₃]+ or [C₈H₁₄(C≡N)₂ minus HC≡N]+,134 [C₈H₁₄(C≡N)₂ minus C₂H₄]+, 122 [C₈H₁₄(C≡N)₂ minus CH₂C≡N]+, 121[C₈H₁₄(C≡N)₂ minus C₃H₅]+, 120 [C₈H₁₄(C≡N)₂ minus C₃H₆]+, 119[C₈H₁₄(C≡N)₂ minus C₃H₇]+, and 105 [C₈H₁₄(C≡N)₂ minus C₄H₉]+ can then beused to identify which of these peaks comprise a C₁₀ dinitrile andthereby quantify the amounts of C₁₀ dinitriles in a process sample by GCanalysis.

Removal of Tertiary-Butylcatechol

Tertiary-butylcatechol (TBC) is a polymerization inhibitor, whichinhibits the polymerization of 1,3-butadiene, particularly while the1,3-butadiene is in storage. Commercial sources of 1,3-butadiene ofteninclude small amounts of TBC to inhibit polymerization of 1,3-butadiene.

TBC may react with certain phosphorus-containing ligands, such asmonodentate phosphite ligands and bidentate phosphite ligands.Hydrocyanation catalysts may comprise phosphorus-containing ligandswhich are reactive with TBC.

European Patent Publication No. 1 344 770 describes problems with TBCreacting with hydrocyanation catalysts comprising phosphite, phosphoniteand phosphinite ligands. The problem is pronounced with bidentateligands, because these ligands tend to be used in small quantities andare expensive. EP 1 344 770 describes the removal of TBC by a variety oftechniques, including vaporization or passing liquid 1,3-butadiene overan absorbent bed, such as alumina.

TBC may be separated from a first catalyst in a liquid/liquid extractionzone. In FIG. 1, this separation takes place in extraction zone 150. TBCwhich enters into the raffinate stream may, in turn, be removed bydistillation. In FIG. 2, TBC, along with methylglutaronitrile is removedfrom adiponitrile in column K₄ via stream 420. However, since TBC tendsto boil at a temperature in between boiling temperatures formethylglutaronitrile and adiponitrile, removal of TBC by distillationmay be difficult and at least a portion of the tertiary-butylcatechol inthe raffinate stream in line 515 may require several passes through thedinitrile recovery loop to be removed. For example,tertiary-butylcatechol may pass into extraction zone 150 along with thedinitrile-enriched stream in line 500. However, sincetertiary-butylcatechol is relatively polar, for example, in comparisonwith cyclohexane, it tends to separate into the raffinate phase inextraction zone 150. In this way, tertiary-butylcatechol is preventedfrom passing downstream, for example, into the third reaction zone (Z₃)shown in FIG. 1. The boiling point of MGN is within the range of 269° C.to 271° C., the boiling point of tertiary-butylcatechol is 285° C., andthe boiling point of adiponitrile is 295° C. Accordingly, by controllingthe distillation conditions in column K₄, at least a portion of anytertiary-butylcatechol in the raffinate stream may be removed along withMGN in line 420.

Removal of Phenolic Compounds

Phenolic compounds, such as phenol and cresols, may be present as acatalyst impurity in catalysts used to react BD with HCN or to isomerize2M3BN. Phenolic compounds may be produced by hydrolysis ofphosphorus-containing ligands. Phenolic compounds may react with ligandsin catalysts used to react 3PN with HCN. Such reactions of phenoliccompounds with catalyst ligands may result in reduced yields orefficiency in the reaction of 3PN with HCN.

Phenolic compounds are removed from reaction streams upstream from areaction zone used to react 3PN with HCN.

Phenolic compounds are separated from a first catalyst in aliquid/liquid extraction zone. In FIG. 1, this separation takes place inextraction zone 150. Phenolic compounds which enter into the raffinatestream may, in turn, be removed by distillation. In FIG. 2, phenoliccompounds are removed from adiponitrile in column K₄ via stream 420.

The first phosphorus-containing ligand, the second phosphorus-containingligand and the third phosphorus-containing ligand may be a ligand whichis reactive with a phenolic compound, such as phenol or cresol. Suchreactive ligands may be a phosphite ligand or a phosphonite ligand or aphosphinite ligand.

A phenolic compound may be an impurity in the source of firstphosphorus-containing ligand. For example, TTP (i.e.tris(tolyl)phosphite) or MTTP may be made by reacting at least onephenolic compound of formula (II) with PCl₃. When the phenolic compoundis an impurity in the source of first phosphorus-containing ligand,phenolic compound is fed into step (a) along with said firstphosphorus-containing ligand.

A phenolic compound may be produced by a hydrolysis reaction, whichdegrades catalyst. Certain phosphorus-containing ligands in catalysts,such as a phosphite ligand or a phosphonite ligand or a phosphiniteligand, react with water to produce a phenolic compound. For example,TTP (i.e. tris(tolyl)phosphite) reacts with water to produce cresols,and MTTP reacts with water to produce a mixture of phenol and cresols. Aphenolic compound and a phosphorus-containing ligand degradation productmay be produced by a hydrolysis reaction occurring upstream of the thirdreaction zone. For example, the hydrolysis reaction may take place inthe first reaction zone or downstream of the first reaction zone, forexample, in a distillation column. A phosphorus-containing liganddegradation product may also be produced by an oxidation reaction orboth an oxidation and hydrolysis reaction occurring upstream of thethird reaction zone.

If water or another protic compound, such as tertiary-butylcatechol, ispresent in the system upstream from the point where the purge stream istaken, phenolic compounds may be produced by hydrolysis or reaction ofthe first phosphorus-containing ligand with a protic compound. Ifphenolic compounds are produced, they may be present in the catalystrecycle stream 140 and the catalyst purge stream 126. Phenoliccompounds, introduced into the first reaction zone (Z₁) along with firstphosphorus-containing ligand, may also be present in the catalystrecycle stream 140 and catalyst purge stream 126. At least a portion ofthe phenolic compounds of formula (II) will be will be extracted intothe raffinate phase in extraction zone 150 along with certain reactionby-products and certain catalyst degradation products, for example,produced by oxidation of the first catalyst.

Removal of Phosphorus-Containing Ligand Degradation Products

When a hydrocyanation catalyst comprises a phosphorus-containing ligand,the ligand may degrade as a result of a hydrolysis or oxidationreaction. Such hydrolysis or oxidation reactions produce unwantedimpurities. Hydrolysis and oxidation products of phosphorus-containingligands are discussed in U.S. Pat. No. 3,773,809.

Phosphorus-containing ligand degradation products are removed fromreaction streams upstream from a reaction zone used to react 3PN withHCN.

Phosphorus-containing ligand degradation products are separated from afirst catalyst in a liquid/liquid extraction zone. In FIG. 1, thisseparation takes place in extraction zone 150. Phosphorus-containingligand degradation products which enter into the raffinate stream may,in turn be removed by distillation. In FIG. 2, Phosphorus-containingligand degradation products are removed from dinitriles in column K₃ viastream 640.

Removal of Methylglutaronitrile (MGN)

When 1,3-butadiene is reacted with hydrogen cyanide to produce3-pentenenitrile, which is a mononitrile compound, small amounts ofdinitrile compounds, including adiponitrile (ADN) andmethylglutaronitrile (MGN), may also be produced. Build-up ofmethylglutaronitrile may cause problems associated with catalystpurification and recycle, catalyst/ligand stability and catalyst thermalsensitivity in reboilers of distillation columns.

Build-up of methylglutaronitrile (MGN) is minimized by a particular wayof removing MGN produced in a reaction of 1,3-butadiene with hydrogencyanide.

MGN is separated from a first catalyst in a liquid/liquid extractionzone. In FIG. 1, this separation takes place in extraction zone 150. MGNwhich enters into the raffinate stream may, in turn, be removed bydistillation. In FIG. 2, MGN is removed from adiponitrile in column K₄via stream 420.

Preventing Lewis Acid from Entering the First Reaction Zone (Z₁)

Pentenenitriles, such as 3-pentenenitrile and 2-methyl-3-butenenitrile,are produced in the reaction of 1,3-butenenitrile with hydrogen cyanidein the presence of a catalyst. However, in this reaction, dinitriles,such as adiponitrile and methylglutaronitrile, are also produced asbyproducts. If Lewis acid promoters are present during this reaction ofBD with HCN, the production of dinitriles, includingmethylglutaronitrile, is increased. When unwanted methylglutaronitrileis produced during the course of reacting 1,3-butadiene with HCN,valuable 1,3-butadiene reactant, which would otherwise be converted towanted adiponitrile, is effectively lost.

3-pentenenitrile and 2-methyl-3-butenenitrile may be separated fromcatalyst and recovered by distillation. The separated catalyst may berecycled. However, dinitriles are more difficult to separate fromcatalyst and tend to build up in the catalyst recycle stream. Build-upof dinitriles in a reactor for hydrocyanating 1,3-butadiene may reducethe effective reactor volume, thereby negatively affecting the reactionefficiency. Also, build-up of dinitriles in concentrated catalystcompositions, such as those present in certain distillation columnbottoms, may cause catalyst to decompose or precipitate.

The consequences of unwanted production of dinitriles and unwantedbuild-up of dinitriles in a catalyst recycle stream are minimized bylimiting the flow of Lewis acid into a reaction zone for reacting1,3-butadiene with hydrogen cyanide. The consequences of unwantedbuild-up of dinitriles in a catalyst recycle stream may further beminimized by removing methylglutaronitrile from the catalyst recyclestream.

Hydrocyanation of 1,3-Butadiene in the First Reaction Zone Z₁

As shown in FIG. 1; 1,3-butadiene (BD) containing feedstock may be fedto the first reaction zone (Z₁), e.g., via line 100, a hydrogen cyanidefeed may be fed to the first reaction zone (Z₁), e.g., via line 120, anda first catalyst may be fed to the first reaction zone (Z₁), e.g., vialine 140.

The 1,3-Butadiene Feedstock

The 1,3-butadiene feedstock may comprise at least 98 wt % 1,3-butadienebased on the total weight of the feedstock, preferably at least 99 wt %,and more preferably at least 99.5 wt %. In one embodiment, the feedstockcomprises from 99.5 to 99.9 wt % 1,3-butadiene based on the total weightof the feedstock. The balance of the feedstock may comprise residuallevels of undesirable impurities, such as butane, butenes, 1,2-butadieneand acetylenes such as propyne. The feedstock may also comprisetertiary-butylcatechol (TBC), for example, 4-tert-butylcatechol. Atleast 95% of the TBC may be present in the form of 4-tert-butylcatechol.A portion of TBC present in the feedstock may optionally be removedbefore charging the 1,3-butadiene to the first reaction step. TheBD-containing feed may comprise less than a total of 100 ppm acetylenes.

The HCN Feed

The HC≡N feed to the first reaction zone (Z₁) and the third reactionzone (Z₃) may be a product of the Andrussow process that is dried toless than about 250 ppm water, for example, less than 125 ppm water, forexample, less than 80 ppm water, by distillation prior to entry intoolefin hydrocyanation reaction zones. However, the HCN feed will usuallycontain at least some water. Very dry HCN is unstable and, for thisreason, it may be undesirable to provide completely anhydrous HCN.Accordingly, the HCN feed may comprise at least 10 ppm, for example, atleast 25 ppm, for example, at least 50 ppm, water.

The hydrogen cyanide (HC≡N) is preferably substantially free of carbonmonoxide, oxygen and ammonia. This HC≡N can be introduced to the firstreaction zone (Z₁) and the third reaction zone (Z₃) as a vapor, liquid,or mixtures thereof; see, for example, European Patent Publication No. 1344 770. As an alternative, a cyanohydrin can be used as the source ofHC≡N; see, for example, U.S. Pat. No. 3,655,723.

Equipment in the First Reaction Zone (Z₁)

The HC≡N feed, the BD-containing feed, and the catalyst composition arecontacted in a reaction zone which may be contained in any suitableequipment known to one skilled in the art. One or more pieces ofconventional equipment may be used to provide the reaction zone, forexample continuous stirred-tank reactors, loop-type bubble columnreactors, gas circulation reactors, bubble column reactors, tubularreactors, or combinations thereof, optionally with apparatus forremoving at least a portion of the heat of reaction.

Reaction Conditions in the First Reaction Zone (Z₁)

A non-oxidizing and anhydrous environment retards oxidative deactivationof the catalyst. Accordingly, a dry inert atmosphere, e.g., nitrogen, isnormally used, although air may be used at the expense of loss of aportion of the catalyst through oxidation and hydrolysis.

The 1,3-butadiene (BD) hydrocyanation is preferably conducted using BDsubstantially free of oxygen, acetylenes and water. BD can be introducedto the hydrocyanation reaction zone as a vapor, liquid, or mixturesthereof; see, for example, European Patent Publication No. 1 344 770. BDmay be at least partially depleted of tertiary-butylcatechol prior tocontacting the catalyst.

The BD hydrocyanation reaction temperature is typically maintainedwithin the range of about −25° C. to about 200° C., for example, withinthe range of about 0° C. to about 150° C. Generally, the reactionpressure should be sufficient to maintain the BD and HC≡N in contactwith the catalyst dissolved in the liquid reaction mixture, with suchpressure at least, in part, being a function of the amount of unreactedBD present in the reaction mixture. Though the disclosed process is notlimited by an upper limit of pressure for this reaction step, forpractical purposes the pressure may generally range from about 15 psiato about 300 psia (about 1.03 bar to about 20.7 bar).

The overall feed molar ratio of the BD to HC≡N may be in the range ofabout 1:1 to about 100:1, for example, in the range of about 1:1 toabout 2:1. Excess BD within the reaction zone may decrease the formationof dinitriles during the BD hydrocyanation reaction.

The feed molar ratio of HC≡N to catalyst in the reaction of HC≡N with BDmay be in the range of about 5:1 to about 100,000:1, for example, in therange about 100:1 to about 5,000:1.

In an embodiment where the first catalyst comprises a monodentateligand, the molar ratio of monodentate ligand to nickel in the catalystfor the reaction of HC≡N with BD may be from about 4:1 to about 50:1,for example, from about 4:1 to about 30:1, for example, from about 4:1to about 15:1.

The residence time in the BD hydrocyanation reaction zone is typicallydetermined by the desire to obtain a certain degree of conversion of BD,HC≡N, or a combination thereof. The BD hydrocyanation reaction zone maycomprise one or more physical reactors. For example, the BDhydrocyanation zone may include one or more plug flow reactors incombination with one or more continuous stirred tank reactors. When areactor is used that substantially provides the mixing characteristicsof a continuous stirred tank reactor, “residence time” is the timenecessary for the combined feeds to displace one reactor volume for thisreaction step. In addition to residence time, catalyst concentration andreaction temperature will also affect conversion of reactants toproducts. Generally, residence times will be in the range of about 0.1hour to about 15 hours, for example, in the range of about 1 hour toabout 10 hours. The HCN conversion may be, for example, greater than99%. Generally, BD conversion in the BD hydrocyanation reaction zone maybe less than 99%, for example, between 80 and 95% overall, for example90% overall. Staged HCN addition within the hydrocyanation reaction zonemay be used.

Distillation of the Reactor Effluent from the First Reaction Zone (Z₁)

The reaction product mixture from the BD hydrocyanation reaction zone,including BD, 3PN, 2M3BN, and catalyst, may be distilled in one or moredistillation apparatus to recover a BD-enriched stream,pentenenitrile-enriched stream including 3PN and 2M3BN, andcatalyst-enriched stream including the catalyst. The BD-enriched andcatalyst-enriched streams may be recycled to the BD hydrocyanationreaction. The pentenenitrile-enriched stream may be further distilled toobtain a 2M3BN-enriched stream and a 2M3BN-depleted stream including3PN.

The 2M3BN-enriched stream from the BD hydrocyanation process may be a2M3BN feed to the 2M3BN isomerization process. In FIGS. 1 and 4, this2M3BN-enriched stream is represented by stream 200. The 2M3BN-depletedstream including 3PN may be used as a 3PN feed to the third reactionzone (Z₃). A 2M3BN-depleted stream including 3PN is represented in FIG.4 as stream 838.

As noted above, the reaction of 1,3-butadiene and hydrogen cyanide inthe presence of a first catalyst in a first reaction zone (Z₁) producesa first reaction effluent (stream 122) comprising 1,3-butadiene,3-pentenenitrile, 2-methyl-3-butenenitrile, and first catalyst. Thesecomponents of the reaction effluent may be separated, at leastpartially, by one or more distillation steps, represented,schematically, by separation section 125 in FIG. 1. An example ofseparation section 125 is shown in greater detail in FIG. 4. Inparticular, these distillation steps may take place in one or moredistillation columns, to provide:

-   -   1) at least one 1,3-butadiene-enriched stream 812 and 824;    -   2) a first 2-methyl-3-butenenitrile-enriched stream 200;    -   3) a first 3-pentenenitrile-enriched stream 838; and    -   4) a first catalyst-enriched stream 140.

These streams are enriched with a particular component in that they havegreater concentrations of these components than the effluent from thefirst reaction zone (Z₁) in line 122. For example, the firstcatalyst-enriched stream 140 has a greater concentration of catalystthan the effluent stream in line 122. The first2-methyl-3-butenenitrile-enriched stream 200 and first3-pentenenitrile-enriched stream 838 may each contain less than a totalof 500 parts per million by weight of phosphorus-containing ligand, forexample, less than 350 parts per million by weight ofphosphorus-containing ligand, for example, less than 200 parts permillion by weight of phosphorus-containing ligand. If an excessiveamount of dinitriles is present in the effluent from the first reactionzone (Z₁), catalyst may thermally degrade, causing the nickel/ligandcomplex to disassociate in column bottoms of distillation apparatus usedto obtain the first catalyst-enriched stream 140.

At least partial separation of a 3-pentenenitrile and2-methyl-3-butenenitrile mixture from at least one phosphorus-containingligand may be achieved by a distillation process. For example, thisseparation may be facilitated by a distillation apparatus comprising afeed inlet; an upper draw outlet; and a bottom draw outlet. Aphosphorus-containing ligand stream, such as stream 813 comprising 3PN,2M3BN, and at least one catalyst including a phosphorus-containingligand, may be flowed into a feed stage of the first distillationapparatus through the feed inlet. The distillation apparatus may includea stripping section, a rectifying section or both. There may be at leastone stage of separation between the feed inlet and the upper drawoutlet. A pentenenitrile-enriched stream comprising 3-pentenenitrile and2-methyl-3-butenenitrile may be withdrawn from the upper draw outlet.This stream is depleted of the at least one phosphorus-containingligand, relative to the phosphorus-containing ligand stream fed to thedistillation column. A pentenenitrile-depleted stream may be withdrawnfrom the bottom draw outlet. This pentenenitrile-depleted stream isenriched with the phosphorus-containing ligand, relative to thephosphorus-containing ligand stream fed to the distillation column. Thefirst distillation apparatus may be operated such that thepentenenitrile-depleted stream comprises at least 5% by weight ofpentenenitrile including the sum of 3-pentenenitrile and2-methyl-3-butenenitrile.

The pentenenitrile-enriched stream comprising 3-pentenenitrile and2-methyl-3-butenenitrile may be distilled in a second distillationapparatus to obtain a 2-methyl-3-butenenitrile-enriched stream as a topproduct and a 2-methyl-3-butenenitrile-depleted stream (i.e. a3-pentenenitrile-enriched stream) as a bottom product.

The first 3-pentenenitrile-enriched stream may comprise small amounts of2-methyl-3-butenenitrile. These small amounts of2-methyl-3-butenenitrile may be separated from 3-pentenenitrile in oneor more distillations columns, where 2-methyl-3-butenenitrile isrecovered as a top product and 3-pentenenitrile is recovered as a bottomproduct. For example, two or more 3-pentenenitrile-enriched streams maybe combined and distilled in a single or shared distillation column orthese streams may be distilled in separate distillation columns.2-methyl-3-butenenitrile recovered from such distillation may be passedas feed to the second reaction zone (Z₂), and 3-pentenenitrile recoveredfrom such distillation may be passed as feed to the third reaction zone(Z₃).

Distillation of the Effluent from Z₁ to Optimize Removal of IntermediateBoilers

Removal of intermediate boilers, such as MGN, C₈H₁₃C≡N compounds, phenoland cresols, from the reaction system may be facilitated by distillingthe reaction product stream from the first reaction zone (Z₁) in aparticular manner. For example, after removing unreacted 1,3-butadieneand hydrogen cyanide from the reaction product stream from the firstreaction zone (Z₁), the stream, comprising pentenenitriles, zero valentnickel and first phosphorus-containing ligand, may be fed into adistillation column having a feed inlet, an upper draw outlet, and abottom draw outlet. The distillation column may have a strippingsection, a rectifying section or both. A rectifying section comprisingat least one stage of separation is provided between the feed inlet andthe upper draw outlet. A pentenenitrile-enriched stream is withdrawnfrom the upper draw outlet. A catalyst-enriched stream is withdrawn fromthe bottom draw outlet. The distillation column is operated in a mannersuch that the catalyst-enriched stream comprises at least 5% by weightof pentenenitrile including the sum of 3-pentenenitrile and2-methyl-3-butenenitrile. In this way, intermediate boilers tend to passinto the catalyst-enriched stream. These compounds may then be removedat least in part from the reaction system by the extraction process intothe raffinate and from the raffinate by the raffinate treatment processdescribed above.

In a modification of this process for distilling the reaction productstream from the first reaction zone (Z₁) depleted of 1,3-butadiene andhydrogen cyanide, the distillation column is further provided with aside draw outlet. A rectifying section comprising at least two stages ofseparation is provided between the feed inlet and the upper draw outlet.A pentenenitrile-enriched stream is withdrawn from the upper drawoutlet. A catalyst-enriched stream is withdrawn from the bottom inlet.The distillation column is further provided with a liquid collectionapparatus, such as a chimney tray, in the rectifying section. Liquid inthe liquid collection apparatus of the rectifying section is collectedat a location between the feed stage and upper draw outlet. At least aportion of the collected liquid is withdrawn to obtain the side-drawstream. The distillation column may be operated in a manner such thatthe catalyst-enriched stream comprises at least 5% by weight ofpentenenitrile including the sum of 3-pentenenitrile and2-methyl-3-butenenitrile. The distillation column may also be operatedin a manner such that dinitriles and intermediate boilers, such as MGN,C₈H₁₃C≡N compounds, phenol and cresols, tend to pass out of the columnthrough the side draw outlet. The stream from the side draw may then bepassed either directly or indirectly into an extraction system. Inanother embodiment, the stream from the side draw is passed to adistillation column to selectively remove phenols, cresols and C₈H₁₃C≡Ncompounds. In this way, at least a portion of the C₈H₁₃C≡N compounds,phenol and cresols are separated from recycled catalyst.

Recycle and Purification of the First Catalyst

The first catalyst-enriched stream passes from separation section 125through line 140. A portion of this catalyst enriched stream in line 140is withdrawn forming a first catalyst purge stream, which passes throughline 126. This purge stream comprises the first catalyst, catalystdegradation product and reaction byproduct. At least a portion of thefirst catalyst from the first catalyst purge in line 126 is fed to afirst catalyst regeneration zone comprising liquid-liquid extraction toat least partially separate catalyst degradation product and reactionbyproduct from the first catalyst.

At least 80%, preferably at least 90%, for example, 93 to 96%, at least99%, at least 99.9%, and substantially all of the first catalyst instream 140 is recycled. A portion of the first catalyst recycle stream140 is withdrawn in purge stream 126 for purification and recovery. Inembodiments of the disclosed process, the minimum amount of circulatingcatalyst that is withdrawn, purified, recovered and optionally treatedto increase its nickel content is selected from 2, 5, 10, 15 and 20% byweight of the circulating catalyst. In other embodiments, less than 100,75, 50 and 25% by weight of the circulating catalyst can be withdrawn,purified, recovered and optionally treated to increase its nickelcontent. The purified and recovered catalyst is then returned to eitherthe first (Z₁) or second (Z₂) reaction zone.

The purification steps as applied to the first and third catalysts aresegregated, in order to avoid (at least reducing to de minimis levels asdescribed herein above) co-mingling of the first catalyst with the thirdcatalyst in the first (Z₁) and second (Z₂) reaction zones, and also thethird (Z₃) reaction zone.

The process conducted in a catalyst regeneration zone may comprise thesteps of:

-   -   1) introducing a dinitrile stream comprising dinitrile and an        extraction solvent stream comprising extraction solvent into an        extraction zone;    -   2) contacting the catalyst purge with extraction solvent from        the extraction solvent stream and dinitrile from the dinitrile        stream in the extraction zone to obtain within the extraction        zone at least two immiscible liquid phases including an extract        phase and a raffinate phase;    -   3) withdrawing from the extract phase an extract stream        comprising extraction solvent and catalyst;    -   4) withdrawing from the raffinate phase a raffinate stream        comprising dinitrile, catalyst degradation product and reaction        byproduct;    -   5) distilling the extract stream to obtain at least one        extraction solvent-enriched stream and an extraction        solvent-depleted stream (i.e. a catalyst-enriched stream)        comprising separated catalyst; and    -   6) optionally, distilling the raffinate phase in one or more        steps to purge catalyst degradation products and to provide a        dinitrile stream depleted in such catalyst degradation products.        Catalyst degradation products may have lower or higher boiling        points than the adiponitrile, and this optional distillation        step may be configured accordingly by one of ordinary skill        given the vapor-liquid equilibrium data for the components to be        distilled.

Purification or regeneration of catalyst results in removal of catalystdegradation products. Such catalyst degradation products may include oneor more of, for example, one or more phosphorus-containing ligandhydrolysis products, e.g., phenol and substituted phenol, one or morephosphorus-containing ligand oxidation products, such as phosphatesderived from the oxidation of phosphite ligands, Ni(C≡N)₂, ligandhydrolysis products and nickel metal.

Purification or regeneration of catalyst also results in removal ofreaction byproducts. Examples of such reaction byproducts include aC₈H₁₃C≡N compound, 2-methyl-2-butenenitrile, 2-pentenenitrile,2-methylglutaronitrile, and ethylsuccinonitrile.

The First Extraction Zone

A first extraction zone is shown in FIG. 1. A catalyst purge stream 126is fed into liquid/liquid extraction zone 150. A non-polar solvent, suchas an alkane, is fed into the liquid/liquid extraction zone 150 throughline 130. A polar solvent, which is immiscible with the non-polarsolvent, is also fed into the liquid/liquid extraction zone 150 throughline 500. The polar solvent introduced into extraction zone 150 throughline 500 comprises adiponitrile. The catalyst purge stream 126 comprisesreaction byproducts and catalyst degradation byproducts formed in thefirst reaction zone (Z₁). In extraction zone 150, there is formed anon-polar phase comprising non-polar solvent and catalyst and a polarphase (e.g., a raffinate) comprising polar solvent and, for example,reaction byproducts and catalyst degradation products. The non-polarphase is taken from extraction zone 150 via line 134 to distillationcolumn 155. The polar phase is taken from extraction zone 150 via line510 to separation section 1000.

The extraction solvent provided to the extraction zone may be at leastone hydrocarbon compound selected from the group consisting of linearaliphatic, branched aliphatic, unsubstituted cycloaliphatic, andalkyl-substituted cycloaliphatic hydrocarbons. Such extraction solventsmay boil in the range of 30° C. to 135° C., for example, from 60° C. to100° C., at a pressure of one atmosphere. The dinitrile feed to theextraction zone may be mainly composed of adiponitrile. MGN and ESN maybe at least partially removed from the dintrile stream prior torecycling to the liquid/liquid extraction zone.

The extraction zone may comprise a plurality of extraction stages. Acatalyst purge stream and, optionally, a side-draw stream comprisingintermediate boilers may be charged into different extraction stages ofthe extraction zone. The side-draw stream may be generated during thedistillation of pentenenitriles containing catalyst to obtain apentenenitrile-enriched stream as an upper draw and a catalyst-enrichedstream as a lower draw. Both the catalyst purge stream and the side-drawstream may comprise dinitriles and intermediate boilers, such asC₈H₁₃C≡N compounds, phenol and cresols. Extract and raffinate phases mayflow in a counter-current fashion within the extraction zone. Theabove-mentioned side-draw stream comprising intermediate boilers may becharged into a multiple stage extraction zone and into an extractionstage closer than the first stage to the extraction stage where theraffinate phase is withdrawn. Extraction solvent may be charged to thesame extraction stage of the extraction zone where the raffinate phaseis withdrawn from the extraction zone to obtain the raffinate stream.The catalyst-enriched stream may be charged to the same extraction stageof the extraction zone where the extract phase is withdrawn from theextraction zone to obtain the extract stream. In a multistage extractionzone, a portion of the catalyst enriched stream may also be charged tothe same extraction stage of the extraction zone where the raffinatephase is withdrawn from the extraction zone to obtain the raffinatestream.

A stream comprising make-up catalyst from a make-up catalyst reactor mayalso be introduced to the catalyst loop downstream of the extractionzone. In a multi-stage extraction zone, comprising, for example, atleast 3, for example, at least 4, for example, at least 5 extractionstages, make-up phosphite ligand of the catalyst may be introduced nearthe stage where the catalyst purge stream is charged.

In the extraction zone, wherein an extract phase and a raffinate phaseare produced, the molar ratio of total moles of mononitrile compoundsdivided by total moles of dinitrile compounds should be sufficient toachieve this phase separation. For example, this molar ratio may bebetween 0 and 0.5, for example, 0.005 to 0.5, for example, 0.01 to 0.25,for example, 0.05 to 0.20, for example, 0.05 and 0.15, for example, 0.1and 0.5. The mononitriles in the extraction zone may include4-pentenenitrile, 3-pentenenitrile, 2-pentenenitrile,2-methyl-3-butenenitrile, 2-methyl-2-butenenitrile, and valeronitrile.The dinitriles in the extraction zone may include adiponitrile,2-methylglutaronitrile, and ethylsuccinonitrile. In order to achieveproper extraction of catalyst into the extraction solvent phase, theflow of catalyst enriched stream into the extraction zone and the flowof the extraction solvent phase from the extraction zone should becontrolled. Also, the flow of catalyst enriched stream into theextraction zone and the flow of the extraction solvent into theextraction zone should be controlled. For example, the ratio of massflow of extraction solvent entering the extraction zone divided by sumof the mass flows of the dinitrile and catalyst feed to the extractionzone for the contacting may be less than about 2, for example, less than1.5, for example, less than 1.2. Further, the flow of raffinate streamwithdrawn from the extraction zone and the flow of the catalyst streaminto the extraction zone should be controlled. For example, the ratio ofmass flow of raffinate stream withdrawn from the extraction zone dividedby mass flow of the pentenenitrile-depleted stream entering theextraction zone for the contacting may be greater than about 0.9. U.S.Pat. No. 3,773,809 to Walter teaches an example of a suitableliquid/liquid extraction process.

The temperature in the extraction zone to facilitate phase separationand catalyst extraction may be from 25° C. to 135° C., for example, 25°C. to 90° C., for example, 50° C. to 75° C. The concentration ofmononitriles in the extraction zone (e.g., from the combined catalystenriched stream and dinitrile stream) may be between 2-20%, for example,5-15%, by weight of total mononitriles, for example, where themononitrile component is calculated as the sum of the weights ofmononitrile compounds comprising 2-pentenenitrile, 3-pentenenitrile,4-pentenenitrile, 2-methyl-3-butenenitrile, 2-methyl-2-butenenitrile,and valeronitrile.

Recycle of Extraction Solvent

Non-polar solvent may be distillatively recovered and recycled to theextraction zone for purifying (i.e. regenerating) catalyst. For example,as shown in FIG. 1, non-polar solvent may be distillatively recovered indistillation column 155 and returned to extraction zone 150, via line130. Extraction zone 150, line 134, distillation column 155 and line130, collectively, form a recovery loop for recycling non-polar solventinto extraction zone 150. Extraction zone 150, line 510, separationsection 1000 and line 500, collectively, form a recovery loop forrecycling polar solvent into extraction zone 150.

The extract stream may be distilled in at least one distillation columnat 1 psia to 22 psia (0.07 bar to 1.5 bar) pressure and with a basetemperature of less than about 160° C., for example, less than about150° C., for example, less than about 140° C. The base temperature ischosen in part to maintain the thermal stability of the catalystcomposition.

Distillation of the Raffinate from the First Reaction Zone (Z₁)

The raffinate stream from the extraction zone may be distilled in one ormore distillation columns to separate dinitriles from other componentsof the raffinate stream, such as extraction solvent, pentenenitriles,reaction byproducts and catalyst degradation products. Dinitrilesseparated from the other components of the raffinate stream may then berecycled to the extraction zone.

Distillation of the raffinate phase is shown in FIG. 2, as describedabove.

Although a majority of the extraction solvent separates into the solventphase in the extraction zone, some extraction solvent is extracted intothe raffinate phase. The raffinate stream, therefore, comprises someextraction solvent. The raffinate stream may further comprise one ormore of at least one pentenenitrile (typically a mixture ofpentenenitriles), tertiary-butylcatechol, C₈H₁₃C≡N compounds, phenol,cresols, and dinitriles comprising adiponitrile (ADN) andmethylglutaronitrile (MGN). In a first distillation step of theraffinate stream, extraction solvent having a lower boiling point thanpentenenitriles may be separated from other higher boiling constituentsof the raffinate stream to obtain an extraction solvent depletedraffinate stream. Such extraction solvents may have a boiling point of,for example, 30 to 135° C., for example, 60 to 100° C. An example ofsuch an extraction solvent is cyclohexane, which has a boiling point(BP) of 81° C.

In a second distillation step of the raffinate stream, pentenenitrilemay be removed from other higher boiling components of the raffinatestream to obtain a pentenenitrile-depleted raffinate stream. Thispentenenitrile-depleted raffinate stream may comprise, for example, atotal of at least 0.01%, for example, at least 0.07%, for example, atleast 0.1%, for example, less than 1%, by weight of pentenenitrileincluding the sum of 4-pentenenitrile, 3-pentenenitrile, and2-pentenenitrile. Examples of pentenenitriles, which may be removed asan overhead stream in this second distillation step include2-methyl-3-butenenitrile, trans-3-pentenenitrile, cis-3-pentenenitrile,trans-2-pentenenitrile, and cis-2-pentenenitrile. Such removedpentenenitriles may have an approximate boiling point within the rangeof from 120° C. to 150° C. The column may be operated under conditionssufficient to keep a majority of the intermediate boilers, such as C₉mononitriles, in the pentenenitrile-depleted stream. These conditionsmay involve operating the column such that at least some pentenenitrileis included in the pentenenitrile depleted stream.

The pentenenitrile-depleted raffinate stream obtained in theabove-mentioned second distillation step may be introduced into at leasta third distillation step. In this third distillation step, compositionshaving a higher boiling point than dinitriles are separated as a bottomstream from the dinitriles and compounds, such astertiary-butylcatechol, C₈H₁₃C≡N compounds, phenol and cresols, ifpresent. Such bottoms products may have a boiling point of, for example,at least 300° C. In contrast, most dinitriles in thepentenenitrile-depleted raffinate stream from the above-mentioned seconddistillation step would tend to have a boiling point within theapproximate range of 260° C. to 300° C.

The third distillation step of the raffinate stream may occur in one ormore distillation columns. In an example of using a single distillationcolumn for this third distillation step, compounds having a boilingpoint of, for example, less than 250° C. are withdrawn as an overheadstream, compounds having a boiling point of, for example, from 260° C.to 300° C. are withdrawn as a side draw from the distillation column,and compounds having a boiling point of, for example, greater than 300°C. are withdrawn as a bottom stream. In this example of a thirddistillation step, the overhead stream may comprise compounds, such asC₈H₁₃C≡N compounds, phenol and cresols, the side stream may comprisecompounds, such as tertiary-butylcatechol and dinitriles, and thebottoms stream may comprise compounds, such as catalyst degradationproducts, including for example, Ni(CN)₂ and an organophosphate formedby oxidation of an organophosphite ligand. For example,tris(tolyl)phosphate is an oxidation byproduct of tris(tolyl)phosphite.

This separation may also take place in two distillation columns. Whentwo distillation columns are used for the third distillation step, afirst distillation column may be operated to produce a bottoms streamcomprising compounds having a boiling point of greater than 300° C. andan overhead stream comprising dinitriles and, for example, C₈H₁₃C≡Ncompounds, phenol and cresols. This overhead stream may then be passedto a second distillation column to produce dinitriles as a bottomsstream and an overhead stream comprising C₈H₁₃C≡N compounds, phenol andcresols.

When the dinitrile stream from the third distillation step comprisesmethylglutaronitrile (MGN), in particular, 2-methylglutaronitrile(2-MGN), this stream may be further distilled to remove MGN from thisstream to thereby produce a stream enriched in adiponitrile for recycleto the extraction zone. 2-MGN has an approximate boiling point of 269°C. to 271° C., whereas adiponitrile has an approximate boiling point of295° C. Tertiary-butylcatechol, especially 4-tertiary-butylcatechol, hasa boiling point of 285° C. The overhead cut point of the above-mentionedthird distillation step for treating the raffinate stream may also beadjusted such that MGN is removed along with C₈H₁₃C≡N compounds, phenoland cresols, as an overhead of the single distillation column with aside draw or as an overhead in of the second distillation column, whentwo columns are used. Removing MGN from the adiponitrile preventsunwanted buildup of MGN. The removal of MGN also facilitates the removalof C₈H₁₃C≡N compounds, phenol and cresols from the catalyst recyclestream and the entire reaction system. Removing MGN further facilitatesremoval of any 2-ethylsuccinonitrile, an isomer of ADN and MGN. Theboiling point of 2-ethylsuccinonitrile is 264° C. At least a portion ofany tertiary-butylcatechol in the dinitrile stream may be removed withthe MGN. The MGN-containing stream recovered from the distillationcolumn may be further purified by removing impurities, such as phenols,cresols and TBC. The purified MGN may be commercially sold. MGN isuseful as a solvent/intermediate in the fiber industry.

Although particular distillation steps are described above forconverting the raffinate stream from the extraction zone into a purifiedadiponitrile stream, which is, in turn, recycled to the extraction zone,it will be understood that other distillation steps are possible. It iswithin the ordinary skill in the art to design and operate such steps.Streams of compounds removed from the adiponitrile in the raffinate maybe disposed of, further refined, used in a different reaction process orrecycled to an appropriate point in the overall reaction system.

Bottoms comprising catalyst degradation products from the above-mentionthird distillation step may passed to a wiped film evaporator (WFE) torecover adiponitrile in such bottoms. A wiped film evaporator may alsobe used to recover adiponitrile from catalyst degradation products in anadiponitrile recovery section 3000. Catalyst degradation products fromseparation section 1000 and separation section 2000 may be fed to awiped film evaporator in adiponitrile recovery section 3000 to recoveradiponitrile in all of the concentrated catalyst degradation products,separated from dinitriles in these sections.

Introduction of Recycled Catalyst into the First Reaction Zone (Z₁)

After catalyst has passed through a distillation apparatus fordistilling non-polar solvent from catalyst, the purified (i.e.regenerated) catalyst may be recycled to the first reaction zone. Whenthe first and second catalysts comprise the same phosphorus-containingligand, at least a portion of the purified (i.e. regenerated), secondcatalyst may be recycled to the first reaction zone. For example,referring to FIG. 1, column bottoms from distillation column 155 includepartially purified catalyst. This partially purified catalyst may betaken from distillation column 155 through lines 156 and 146 forintroduction into catalyst recycle line 140 for recycle into the firstreaction zone (Z₁). Optionally, a side stream may be taken from line 246into line 200 or 240, and this side stream may be used as a catalystfeed to the second reaction zone (Z₂). Any partially purified stream offirst catalyst, which is subsequently fed to the second reaction zone(Z₂), may be provided with additional zero-valent Ni, for example,and/or first phosphorus-containing ligand, via line 245. Although notshown in FIG. 1, line 245 may optionally be fed directly into line 246or line 248 instead of line 240.

The composition of the column bottoms from column 155 in line 156 maycomprise, for example, 1-2 wt % zero valent Ni, 70-90 wt %phosphorus-containing ligand, less than 4 wt % of the non-polar solvent,such a cyclohexane, used in the extraction zone 150, less than 10 wt %pentenenitriles, and less than 10 wt % dinitriles.

Isomerization of 2-Methyl-3-Butenenitrile in the Second Reaction Zone(Z₂)

As shown in FIG. 1, 2-methyl-3-butenenitrile (2M3BN)) containingfeedstock may be fed to the second reaction zone (Z₂), e.g., via line222, and a second catalyst may be fed to the second reaction zone (Z₂),e.g., via line 240.

In a second reaction zone (Z₂) at least a portion of the first2-methyl-3-butenenitrile-enriched stream is reacted in the presence of asecond catalyst, comprising a zero-valent nickel and at least onephosphorus-containing ligand. In FIG. 1, this first2-methyl-3-butenenitrile-enriched stream passes from separation section125 to the second reaction zone (Z₂) through line 200. FIG. 1 does notshow lines for withdrawing the above-mentioned first3-pentenenitrile-enriched stream and 1,3-butadiene-enriched stream fromseparation section 125. The first 3-pentenenitrile-enriched stream may,for example, by-pass the second reaction zone (Z₂) and be fed directlyinto the third reaction zone (Z₃) or to a feed line, such as line 300,shown in FIG. 1 for introducing feed into the third reaction zone (Z₃).As mentioned above, the 1,3-butadiene-enriched stream may be recycledback into the first reaction zone (Z₁).

The 2-Methyl-3-Butenenitrile Feed

The 2-methyl-3-butenenitrile feed to the second reaction zone (Z₂) isobtained from distillation steps described herein above. This feed maycomprise at least 30 wt % 2M3BN. This feed may also comprise less than70 wt % of pentenenitriles other than 2M3BN, and less than 1 wt % of thefirst phosphorus-containing ligand, for example, less than 0.1 wt. %.

Equipment in the Second Reaction Zone (Z₂)

The 2M3BN-containing feed and the catalyst composition are contacted ina reaction zone which may be contained in any suitable equipment knownto one skilled in the art. One or more pieces of conventional equipmentmay be used to provide the reaction zone, for example continuousstirred-tank reactors, loop-type bubble column reactors, gas circulationreactors, bubble column reactors, tubular reactors, or combinationsthereof, optionally with apparatus for removing at least a portion ofthe heat of reaction.

Reaction Conditions in the Second Reaction Zone (Z₂)

The feed molar ratio of 2M3BN to catalyst for the isomerization reactionstep is generally greater than 1:1, usually in the range from about 5:1to 20,000:1, for example, from about 100:1 to about 5,000:1.

When a monodentate ligand is used, the molar ratio of monodentate ligandto zero valent nickel in the catalyst for the isomerization reaction maybe from about 1:1 to about 50:1, for example, from about 1:1 to about30:1. When a bidentate ligand is used, the molar ratio of bidentateligand to zero valent nickel in the catalyst for the isomerizationreaction may be from 1:1 to 10:1, for example, from 1:1 to 5:1.

The residence time in the reaction zone for the isomerization reactionmay be from about 0.1 hour to about 15 hours, for example, from about 1hour to about 10 hours.

For the isomerization of 2M3BN to produce 3PN, the reaction temperaturemay be maintained within the range of about 0° C. to about 200° C., forexample, within the range of about 50° C. to about 165° C. Again, thoughthe invention is not limited by an upper limit of pressure for thisreaction step, for practical purposes the pressure generally ranges fromabout 15 psia to about 300 psia (about 1.03 bar to about 20.7 bar).

Distillation of the Reactor Effluent from the Second Reaction Zone (Z₂)

The reaction product mixture from the 2M3BN isomerization reaction zonemay include certain light boilers, 3PN, 2M3BN, (Z)-2M2BN and catalyst.At least some of the light boilers may be removed in a firstdistillation step. Then, a stream depleted in light boilers may bedistilled in one or more distillation apparatus to recover a(Z)-2M2BN-enriched stream, a (Z)-2M2BN-depleted stream including 3PN and2M3BN, and a catalyst-enriched stream including the catalyst. At least aportion of the catalyst-enriched stream may be recycled to the 2M3BNisomerization reaction.

The (Z)-2M2BN-depleted stream may be further distilled to obtain a2M3BN-enriched stream and a 2M3BN-depleted stream including 3PN. The2M3BN-enriched stream from the BD hydrocyanation process may be a 2M3BNfeed to the 2M3BN isomerization process.

The effluent from the second reaction zone (Z₂) comprises3-pentenenitrile, 2-methyl-3-butenenitrile and the second catalyst. InFIG. 1, this effluent from the second reaction zone (Z₂) passes throughline 222. These components of the reaction effluent may be separated, atleast partially by one or more distillation steps, represented,diagrammatically, by separation section 225 in FIG. 1. An example ofseparation section 225 is shown in greater detail in FIG. 5. Inparticular, these distillation steps may take place in one or moredistillation columns, to provide:

-   -   1) a second 2-methyl-3-butenenitrile-enriched stream 967;    -   2) a second 3-pentenenitrile-enriched stream 300; and    -   3) a second catalyst-enriched stream 240.

The second 2-methyl-3-butenenitrile-enriched stream and the second3-pentenenitrile-enriched stream may each contain less than a total of500 parts per million by weight of the phosphorus-containing ligand. Forexample, the second 3-pentenenitrile-enriched stream may contain lessthan 300 ppm, for example, less than 100 ppm, of thephosphorus-containing ligand.

The second 3-pentenenitrile-enriched stream may comprise small amountsof 2-methyl-3-butenenitrile. These small amounts of2-methyl-3-butenenitrile may be separated from 3-pentenenitrile in oneor more distillations columns, where 2-methyl-3-butenenitrile isrecovered as a top product and 3-pentenenitrile is recovered as a bottomproduct. For example, the first and second 3-pentenenitrile-enrichedstreams may be combined and distilled in a single or shared distillationcolumn or these streams may be distilled in separate distillationcolumns. 2-methyl-3-butenenitrile recovered from such distillation maybe passed as feed to the second reaction zone (Z₂), and 3-pentenenitrilerecovered from such distillation may be passed as feed to the thirdreaction zone (Z₃).

The second 3-pentenenitrile-enriched stream may further comprise(Z)-2-methyl-2-butenenitrile and the second 3-pentenenitrile-enrichedstream may be distilled to obtain a(Z)-2-methyl-3-butenenitrile-enriched stream, comprising2-methyl-3-butenenitrile and (Z)-2-methyl-2-butenenitrile, along withother low boilers as described previously, as a top product, and a(Z)-2-methyl-2-butenenitrile-depleted stream, comprising3-pentenenitrile, 2-methyl-3-butenenitrile, and, depending ondistillation conditions, some (Z)-2-methyl-2-butenenitrile, as a bottomproduct.

At least one distillation system for distilling the effluent from thesecond reaction zone (Z₂) is described above. However, it will beunderstood that it is within the skill in the art to design and operateother distillation systems to achieve the same or essentially the sameresults. For example, a stream comprising 3PN and 2M3BN obtained bydistilling the effluent from the second reaction zone (Z₂) may be passedto a distillation apparatus, such as distillation apparatus 830, used inthe distillation of the effluent form the from the first reaction zone(Z₁), to obtain a 3PN-enriched stream and a 2M3BN-enriched stream.

At least a portion of the second 3-pentenenitrile-enriched stream may beused to prepare a catalyst solution. In particular, at least a portionof the second 3-pentenenitrile-enriched stream may be passed into acatalyst reaction zone, wherein nickel metal reacts with thephosphorus-containing ligand to produce a catalyst solution, comprisingcatalyst and pentenenitriles. A portion of this catalyst solution may bepassed into the second reaction zone (Z₂). When the first and secondcatalysts comprise the same phosphorus-containing ligand, a portion ofthe catalyst may be passed to the first reaction zone (Z₁).

Recycle and Purification of the Second Catalyst

The second catalyst-enriched stream passes from separation section 225through line 240. A portion of this catalyst enriched stream in line 240is withdrawn forming a second catalyst purge stream, which passesthrough line 226. This purge stream comprises the second catalyst,catalyst degradation product and reaction byproduct. At least a portionof the second catalyst from the second catalyst purge stream in line 226may be fed to a second catalyst regeneration zone comprisingliquid-liquid extraction to at least partially separate catalystdegradation product and reaction byproduct from a separated firstcatalyst. According to an option not shown in FIG. 1, at least a portionof the second catalyst purge in line 226 may be fed to a first catalystregeneration zone. In such an option, the second catalyst regenerationzone may be omitted.

At least 10%, for example, at least 50%, for example, 75%, for example,80% to 90%, of the second catalyst in stream 240 is recycled, and theremaining amount in purge stream 226 is withdrawn for purification andrecovery. In one embodiment, 20 to 60% by weight of the circulatingcatalyst can be withdrawn, purified, recovered and optionally treated toincrease its nickel content. The purified and recovered catalyst is thenreturned to either the first (Z₁) or second (Z₂) reaction zone.Depending upon the activity of the second catalyst, one embodiment ofthe disclosed process may include charging the second catalyst to thesecond reaction zone (Z₂) and not recycling it.

The process conducted in a catalyst regeneration zone may comprise thesteps of:

-   -   1) introducing a dinitrile stream comprising dinitrile and an        extraction solvent stream comprising extraction solvent into an        extraction zone;    -   2) contacting the catalyst purge with extraction solvent from        the extraction solvent stream and dinitrile from the dinitrile        stream in the extraction zone to obtain within the extraction        zone at least two immiscible liquid phases including an extract        phase and a raffinate phase;    -   3) withdrawing from the extract phase an extract stream        comprising extraction solvent and catalyst;    -   4) withdrawing from the raffinate phase a raffinate stream        comprising dinitrile, catalyst degradation product and reaction        byproduct;    -   5) distilling the extract stream to obtain at least one        extraction solvent-enriched stream and an extraction        solvent-depleted stream (i.e. a catalyst-enriched stream)        comprising separated catalyst; and    -   6) optionally, distilling the raffinate phase in one or more        steps to purge catalyst degradation products and to provide a        dinitrile stream depleted in such catalyst degradation products.        Catalyst degradation products may have lower or higher boiling        points than the adiponitrile and this optional distillation step        may be configured accordingly by one of ordinary skill given the        vapor-liquid equilibrium data for the components to be        distilled.

Purification or regeneration of catalyst results in removal of catalystdegradation products. Such catalyst degradation products include one ormore of, for example, one or more phosphorus-containing ligandhydrolysis products, e.g., phenol and substituted phenol, one or morephosphorus-containing ligand oxidation products, such as phosphatesderived from the oxidation of phosphite ligands, Ni(C≡N)₂, ligandhydrolysis products and nickel metal.

Purification or regeneration of catalyst also results in removal ofreaction byproducts. Examples of such reaction byproducts includeC₈H₁₃C≡N compounds, 2-methyl-2-butenenitrile, 2-pentenenitrile,2-methylglutaronitrile, and ethylsuccinonitrile.

The Second Extraction Zone

A second extraction zone is shown in FIG. 1. A catalyst purge stream 226is fed into liquid/liquid extraction zone 250. A non-polar solvent, suchas an alkane, is fed into the liquid/liquid extraction zone 250 throughline 230. A polar solvent, which is immiscible with the non-polarsolvent, is also fed into the liquid/liquid extraction zone 250 throughline 700. The polar solvent introduced into extraction zone 250 throughline 700 comprises reaction byproducts and catalyst degradationbyproducts formed in the first reaction zone (Z₁). In extraction zone250, there is formed a non-polar phase comprising non-polar solvent andcatalyst and a polar phase (e.g., a raffinate) comprising polar solventand, for example, reaction byproducts and catalyst degradation products.The non-polar phase is taken from extraction zone 250 via line 234 todistillation column 255. The polar phase is taken from extraction zone250 via line 710 to separation section 2000.

The extraction solvent provided to the extraction zone may be at leastone hydrocarbon compound selected from the group consisting of linearaliphatic, branched aliphatic, unsubstituted cycloaliphatic, andalkyl-substituted cycloaliphatic hydrocarbons. Such extraction solventsmay boil in the range of 30° C. to 135° C., for example, 60° C. to 100°C., at a pressure of one atmosphere. The dinitrile feed to theextraction zone may be mainly composed of adiponitrile. MGN and ESN maybe removed from the dintrile stream prior to recycle to theliquid/liquid extraction zone. However, even when MGN and ESN areremoved, small amounts of MGN and ESN may still be present, becausethese isomers of adiponitrile may not be completely removed in thedistillation process used to treat the raffinate stream.

The extraction zone may comprise a plurality of extraction stages. Acatalyst purge stream and, optionally, a side-draw stream comprisingintermediate boilers may be charged into different extraction stages ofthe extraction zone. The side-draw stream may be generated during thedistillation of pentenenitriles containing catalyst to obtain apentenenitrile-enriched stream as an upper draw and a catalyst-enrichedstream as a lower draw. Both the catalyst purge stream and the side-drawstream may comprise dinitriles and intermediate boilers, such asC₈H₁₃C≡N compounds, phenol and cresols. Extract and raffinate phases mayflow in a counter-current fashion within the extraction zone. Theabove-mentioned side-draw stream comprising intermediate boilers may becharged into a multiple stage extraction zone and into an extractionstage closer than the first stage to the extraction stage where theraffinate phase is withdrawn. Extraction solvent may be charged to thesame extraction stage of the extraction zone where the raffinate phaseis withdrawn from the extraction zone to obtain the raffinate stream.The catalyst-enriched stream may be charged to the same extraction stageof the extraction zone where the extract phase is withdrawn from theextraction zone to obtain the extract stream. In a multistage extractionzone, a portion of the catalyst enriched stream may also be charged tothe same extraction stage of the extraction zone where the raffinatephase is withdrawn from the extraction zone to obtain the raffinatestream.

A stream comprising make-up ligand may also be introduced into theextraction zone.

In the extraction zone, wherein an extract phase and a raffinate phaseare produced, the molar ratio of total moles of mononitrile compoundsdivided by total moles of dinitrile compounds should be sufficient toachieve this phase separation. For example, this ratio may be between 0and 0.5, for example, 0.005 to 0.5, for example, 0.01 to 0.25, forexample, 0.05 to 0.20, for example, 0.05 and 0.15, for example, 0.1 and0.5. The mononitriles in the extraction zone may include4-pentenenitrile, 3-pentenenitrile, 2-pentenenitrile,2-methyl-3-butenenitrile, 2-methyl-2-butenenitrile, and valeronitrile.The dinitriles in the extraction zone may include adiponitrile,2-methylglutaronitrile, and ethylsuccinonitrile. In order to achieveproper extraction of catalyst into the extraction solvent phase, theflow of catalyst enriched stream into the extraction zone and the flowof the extraction solvent phase from the extraction zone should becontrolled. Ratios of extraction solvents and catalyst charged to theextraction zone are substantially the same as described above forextraction zone 150. The boiling point of the dinitrile may be greaterthan a boiling point of 3-pentenenitrile at a given pressure. Examplesof such dinitrile compounds include adiponitrile,2-methylglutaronitrile, ethylsuccinonitrile, and mixtures of thesedinitriles. The temperature in the extraction zone to facilitate phaseseparation and catalyst extraction may be from 25° C. to 135° C., forexample, for example, 25° C. to 90° C., for example, 50° C. to 75° C.The concentration of mononitriles in the extraction zone (e.g., from thecombined catalyst enriched stream and dinitrile stream) may be between2-20%, for example, 5-15%, by weight of total mononitriles, for example,where the mononitrile component is calculated as the sum of the weightsof mononitrile compounds comprising 2-pentenenitrile, 3-pentenenitrile,4-pentenenitrile, 2-methyl-3-butenenitrile, 2-methyl-2-butenenitrile,and valeronitrile.

Recycle of Extraction Solvent

Non-polar solvent may be distillatively recovered and recycled to theextraction zone for purifying (i.e. regenerating) catalyst. For example,as shown in FIG. 1, non-polar solvent may be distillatively recovered indistillation column 255 and returned to extraction zone 250, via line230. Extraction zone 250, line 234, distillation column 255 and line230, collectively, form a recovery loop for recycling non-polar solventinto extraction zone 250. Extraction zone 250, line 710, separationsection 2000 and line 700, collectively, form a recovery loop forrecycling polar solvent into extraction zone 250.

The extract stream may be distilled in at least one distillation columnat 1 psia to 22 psia (0.07 bar to 1.5 bar) pressure and with a basetemperature of less than about 160° C., for example, less than about150° C., for example, less than about 140° C., for example, less thanabout 130° C., or, for example, less than about 120° C. The basetemperature is chosen in part to maintain the thermal stability of thecatalyst composition.

Distillation of the Raffinate from the Second Reaction Zone (Z₂)

The raffinate stream from the extraction zone may be distilled in one ormore distillation columns to separate dinitriles from other componentsof the raffinate stream, such as extraction solvent, pentenenitriles,reaction byproducts and catalyst degradation products. Dinitrilesseparated from the other components of the raffinate stream may then berecycled to the extraction zone.

Distillation of the raffinate phase is shown in FIG. 2, as describedabove.

Although a majority of the extraction solvent separates into the solventphase in the extraction zone, some extraction solvent is extracted intothe raffinate phase. The raffinate stream, therefore, comprises someextraction solvent. The raffinate stream may further comprise one ormore of at least one pentenenitrile (typically a mixture ofpentenenitriles), tertiary-butylcatechol, C₈H₁₃C≡N compounds, phenol,cresols, and dinitriles comprising adiponitrile (ADN) andmethylglutaronitrile (MGN). In a first distillation step of theraffinate stream, extraction solvent having a lower boiling point thanpentenenitriles may be separated from other higher boiling constituentsof the raffinate stream to obtain an extraction solvent depletedraffinate stream. Such extraction solvents may have a boiling point of,for example, from 30 to 135° C., for example, from 60 to 100° C. Anexample of such an extraction solvent is cyclohexane, which has aboiling point (BP) of 81° C.

In a second distillation step of the raffinate stream, pentenenitrilemay be removed from other higher boiling components of the raffinatestream to obtain a pentenenitrile-depleted raffinate stream. Thispentenenitrile-depleted raffinate stream may comprise, for example, atotal of at least 0.01%, for example, at least 0.07%, for example, atleast 0.1%, for example, less than 1%, by weight of pentenenitrileincluding the sum of 4-pentenenitrile, 3-pentenenitrile, and2-pentenenitrile. Examples of pentenenitriles, which may be removed asan overhead stream in this second distillation step include2-methyl-3-butenenitrile, trans-3-pentenenitrile, cis-3-pentenenitrile,trans-2-pentenenitrile, and cis-2-pentenenitrile. Such removedpentenenitriles may have an approximate boiling point within the rangeof from 120° C. to 150° C.

The pentenenitrile-depleted raffinate stream obtained in theabove-mentioned second distillation step may be introduced into at leasta third distillation step. In this third distillation step, compositionshaving a higher boiling point than dinitriles are separated as a bottomstream from the dinitriles and compounds, such astertiary-butylcatechol, C₈H₁₃C≡N compounds, phenol and cresols, ifpresent. Such bottoms products may have a boiling point of, for example,at least 300° C. In contrast, most dinitriles in thepentenenitrile-depleted raffinate stream from the above-mentioned seconddistillation step would tend to have a boiling point within theapproximate range of 260° C. to 300° C.

The third distillation step of the raffinate stream may occur in one ormore distillation columns. In an example of using a single distillationcolumn for this third distillation step, compounds having a boilingpoint of, for example, less than 250° C. are withdrawn as an overheadstream, compounds having a boiling point of, for example, from 260° C.to 300° C. are withdrawn as a side draw from the distillation column,and compounds having a boiling point of, for example, greater than 300°C. are withdrawn as a bottom stream. In this example of a thirddistillation step, the overhead stream may comprise compounds, such asC₈H₁₃C≡N compounds, phenol and cresols, the side stream may comprisecompounds, such as tertiary-butylcatechol and dinitriles, and thebottoms stream may comprise compounds, such as catalyst degradationproducts, including for example, Ni(CN)₂ and an organophosphate formedby oxidation of an organophosphite ligand. For example,tris(tolyl)phosphate is an oxidation byproduct of tris(tolyl)phosphite.

This separation may also take place in two distillation columns. Whentwo distillation columns are used for the third distillation step, afirst distillation column may be operated to produce a bottoms streamcomprising compounds having a boiling point of greater than 300° C. andan overhead stream comprising dinitriles and, for example, C₈H₁₃C≡Ncompounds, phenol and cresols. This overhead stream may then be passedto a second distillation column to produce dinitriles as a bottomsstream and an overhead stream comprising lower boilers, such as C₈H₁₃C≡Ncompounds, phenol and cresols.

When the dinitrile stream from the third distillation step comprisesmethylglutaronitrile (MGN), in particular, 2-methylglutaronitrile(2-MGN), this stream may be further distilled to remove MGN from thisstream to thereby produce an essentially pure adiponitrile stream forrecycle to the extraction zone. 2-MGN has an approximate boiling pointof 269° C. to 271° C., whereas adiponitrile has an approximate boilingpoint of 295° C. Tertiary-butylcatechol, especially4-tertiary-butylcatechol, has a boiling point of 285° C. The overheadcut point of the above-mentioned third distillation step for treatingthe raffinate stream may also be adjusted such that MGN is removed alongwith C₈H₁₃C≡N compounds, phenol and cresols, as an overhead of thesingle distillation column with a side draw or as an overhead in of thesecond distillation column, when two columns are used. Removing MGN fromthe adiponitrile prevents unwanted buildup of MGN. The removal of MGNalso facilitates the removal of C₈H₁₃C≡N compounds, phenol and cresolsfrom the catalyst recycle stream and the entire reaction system.Removing MGN further facilitates removal of any 2-ethylsuccinonitrile,an isomer of ADN and MGN. The boiling point of 2-ethylsuccinonitrile is264° C. At least a portion of any tertiary-butylcatechol in thedinitrile stream may be removed with the MGN.

Although particular distillation steps are described above forconverting the raffinate stream from the extraction zone into a purifiedadiponitrile stream, which is, in turn, recycled to the extraction zone,it will be understood that other distillation steps are possible. It iswithin the ordinary skill in the art to design and operate such steps.Streams of compounds removed from the adiponitrile in the raffinate maybe disposed of, further refined, used in a different reaction process orrecycled to an appropriate point in the overall reaction system.

Bottoms comprising catalyst degradation products from the above-mentionthird distillation step may passed to a wiped film evaporator (WFE) torecover adiponitrile in such bottoms. A wiped film evaporator may alsobe used to recover adiponitrile from catalyst degradation products in anadiponitrile recovery section 3000. Catalyst degradation products fromseparation section 1000 and separation section 2000 may be fed to asingle wiped film evaporator in adiponitrile recovery section 3000 torecover adiponitrile in all of the concentrated catalyst degradationproducts, separated from dinitriles in these sections.

Introduction of Recycled Catalyst into the Second Reaction Zone (Z₂)

After catalyst has passed through a distillation apparatus fordistilling non-polar solvent from catalyst, the purified (i.e.regenerated), second catalyst may be recycled to the second reactionzone. When the first and second catalysts comprise the samephosphorus-containing ligand, at least a portion of the purified (i.e.regenerated), second catalyst may be recycled to the first reactionzone. When the second and third catalysts comprise the samephosphorus-containing ligand, at least a portion of the purified (i.e.regenerated), second catalyst may be recycled to the third reactionzone. For example, referring to FIG. 1, column bottoms from distillationcolumn 255 include partially purified catalyst. This partially purifiedcatalyst may be taken from distillation column 255 through line 248 forintroduction into catalyst recycle line 240 for recycle into the secondreaction zone (Z₂). Optionally, when the first and second catalystcomprise the same phosphorus-containing ligand, a side stream may betaken from line 248 into line 247, and this side stream may be used as acatalyst feed to the first reaction zone (Z₁). Any partially purifiedstream of second catalyst, which is subsequently fed to the firstreaction zone (Z₁), may be provided with additional zero-valent Ni, forexample, and/or first phosphorus-containing ligand, via line 145.Although not shown in FIG. 1, line 145 may optionally be fed directlyinto line 140 instead of line 146. In an embodiment where secondreaction zone (Z₂) and the third reaction zone (Z₃) share catalyst, themake-up catalyst for the second reaction zone (Z₂) may be recovered fromthe catalyst recycle stream of the third reaction zone (Z₃). Thisembodiment is not illustrated in the Figures.

Hydrocyanation of 3-Pentenenitrile in the Third Reaction Zone Z₃

As shown in FIG. 1, 3-pentenenitrile (3PN) containing feedstock may befed to the third reaction zone (Z₃), e.g., via line 300, a hydrogencyanide feed may be fed to the third reaction zone (Z₃), e.g., via line220, and a third catalyst may be fed to the third reaction zone (Z₃),e.g., via line 340. The catalyst feed also comprises a Lewis acidpromoter.

A first 3-pentenenitrile stream is obtained from the distillation of theeffluent from the first reaction zone (Z₁). A second 3-pentenenitrilestream is obtained from the distillation of the effluent of the secondreaction zone (Z₂). In the third reaction zone (Z₃), at least a portionof the first 3-pentenenitrile-enriched stream and the second3-pentenenitrile-enriched stream is reacted with hydrogen cyanide in thepresence of a third catalyst, comprising a zero-valent nickel and atleast one phosphorus-containing ligand, and at least one promoter. InFIG. 1, the second 3-pentenenitrile-enriched stream passes fromseparation section 225 to the third reaction zone (Z₃) through line 300.FIG. 1 does not show a line for withdrawing the above-mentioned second2-methyl-3-butenenitrile-enriched stream and Z-2M₂BN enriched streamfrom separation section 225. The second2-methyl-3-butenenitrile-enriched stream may, for example, be recycledback into the second reaction zone (Z₂).

The 3-Pentenenitrile Feedstock

The 3-pentenenitrile feed to the third reaction zone (Z₃) is obtainedfrom distillation steps described herein above. This feed may compriseat least 95 wt % 3PN. This feed may also comprise less than 5 wt % ofpentenenitriles other than 3PN, and less than 0.1 wt % of the firstphosphorus-containing ligand.

The 3PN feed may comprise less than 5000 parts per million (ppm) C₉mononitriles, for example, less than 2000 parts per million (ppm) C₉mononitriles, for example, less than 1000 parts per million (ppm) C₉mononitriles, for example, less than 600 parts per million (ppm) C₉mononitriles.

The HCN Feed

The HC≡N feed to the first reaction zone (Z₁) and the third reactionzone (Z₃) may be a product of the Andrussow process that is dried toless than about 250 ppm water, for example, less than 125 ppm water, forexample, less than 80 ppm water, by distillation prior to entry intoolefin hydrocyanation reaction zones. However, the HCN feed will usuallycontain at least some water. Very dry HCN is unstable, and it ispreferred to use anhydrous HCN Accordingly, the HCN feed may comprise atleast 10 ppm, for example, at least 25 ppm, for example, at least 50ppm, water.

The hydrogen cyanide (HC≡N) is preferably substantially free of carbonmonoxide, oxygen and ammonia. This HC≡N can be introduced to the firstreaction zone (Z₁) and the third reaction zone (Z₃) as a vapor, liquid,or mixtures thereof; see, for example, European Patent Publication No. 1344 770. As an alternative, a cyanohydrin can be used as the source ofHC≡N; see, for example, U.S. Pat. No. 3,655,723.

Equipment in the Third Reaction Zone (Z₃)

The HC≡N feed, the 3PN-containing feed, and the catalyst composition arecontacted in a reaction zone which may be contained in any suitableequipment known to one skilled in the art. One or more pieces ofconventional equipment may be used to provide the reaction zone, forexample continuous stirred-tank reactors, loop-type bubble columnreactors, gas circulation reactors, bubble column reactors, tubularreactors, or combinations thereof, optionally with apparatus forremoving at least a portion of the heat of reaction.

Reaction Conditions in the Third Reaction Zone (Z₃)

3PN hydrocyanation may be performed by reacting HC≡N and 3PN as a vapor,liquid, or mixtures thereof. As an alternative, a cyanohydrin may beused as the source of HC≡N.

The steps for making 3-pentenenitrile and the steps reacting3-pentenenitrile with hydrogen cyanide need not take place in the samelocation or facility. For example, the second reaction zone and thethird reaction zone may be separated from each other by a distance of atleast 500 meters. The third reaction zone may be capable of beingoperated separately and independently from the first reaction zone andthe second reaction zone.

In the 3PN hydrocyanation reaction, promoters are provided to enhancethe production of dinitriles. As known in the art, promoters influenceboth catalyst activity and selectivity to the desired ADN. Promotersemployed include salts of metals having atomic numbers 13, 21-32, 39-50,and 57-80, for example, zinc, and compounds of the formula BR′₃ whereinR′ is an alkyl or an aryl radical of up to 18 carbon atoms, for exampletriphenylboron, (C₆H₅)₃B. The anions of the metal salts include halides,for example chloride, sulfates, phosphates, and lower aliphaticcarboxylates. Useful promoters are generally known in the art as Lewisacids. The mole ratio of promoter to nickel in the catalyst issufficient to promote the hydrocyanation of 3-pentenenitrile, and in oneembodiment may be in the range of 1:20 to 50:1, for example, from 0.2:1to 2:1 when the Lewis acid promoter is ZnCl₂.

In the 3PN hydrocyanation process, a 2M3BN-depleted stream from the BDhydrocyanation process, a 2M3BN-depleted stream from the 2M3BNisomerization process, or a combination thereof, is a useful feedstream. The 3PN hydrocyanation reaction temperature may be maintainedwithin the range of about 0° C. to about 150° C., for example, withinthe range of about 25° C. to about 80° C. Generally, the reactionpressure should be sufficient to maintain the HC≡N in contact with thecatalyst dissolved in the liquid reaction mixture. Such pressure is atleast, in part, a function of the amount of unreacted HC≡N present inthe reaction mixture. While an upper limit of pressure for this reactionstep is not limited to any particular pressure, for practical purposesthe pressure generally ranges from about 15 psia to about 300 psia(about 1.03 bar to about 20.7 bar).

The overall feed molar ratio of 3PN to HC≡N may be in the range of 1:1to 100:1, for example, in the range of 1:1 to about 5:1.

The molar ratio of HC≡N to catalyst in the reaction of 3PN with HC≡N maybe in the range of 10:1 to 5000:1, for example, 100:1 to 3000:1, forexample, in the range 300:1 to 2000:1.

The phosphorus-containing ligand used in the reaction of 3PN with HC≡Nis, preferably, a bidentate ligand. The molar ratio of bidentate ligandto nickel in the catalyst for the 3PN hydrocyanation step may be from1:1 to 10:1, for example, 1:1 to 5:1, for example, 1:1 to 3:1.

The residence time in the 3PN hydrocyanation reaction zone for thisreaction step is typically determined by the desire to obtain a certaindegree of conversion of pentenenitriles, HC≡N, or a combination thereof.In addition to residence time, catalyst concentration and reactiontemperature will also affect conversion of reactants to products.Generally, residence times will be in the range of about 0.1 hour toabout 30 hours, for example, in the range of about 1 hour to about 20hours. The HC≡N conversion may be greater than 99%.

Processing of the Reaction Effluent from the Third Reaction Zone (Z₃)

The effluent from the third reaction zone (Z₃) comprises adiponitrile,third catalyst, catalyst promoter and catalyst degradation product. InFIG. 1, this reaction effluent from the third reaction zone (Z₃) passesthrough line 400 to liquid/liquid extraction zone 370. One or morestages of distillation (not illustrated) may be included between thethird reaction zone (Z₃) and liquid/liquid extraction zone 370 to removelower-boiling constituents including unreacted 3-pentenenitrile.Extraction solvent is fed into extraction zone 370 through line 330. Inextraction zone 370 there is formed an extract phase and a raffinatephase. The extract phase comprises the extraction solvent and thirdcatalyst, and the raffinate phase comprises adiponitrile, catalystdegradation products and promoter. The extract phase passes through line334 to distillation column 375, where extraction solvent is separatedfrom the catalyst. The extraction solvent from distillation column 375passes through line 330 and is recycled back into extraction zone 370. Acatalyst stream is taken from distillation column 375 and is recycledback into the third reaction zone (Z₃). The raffinate phase is takenfrom extraction zone 370 through line 600 into adiponitrile purificationsection 3000. A purified adiponitrile product stream is recovered vialine 660.

The reaction product mixture from the 3PN hydrocyanation reaction zone,including pentenenitriles, such as 3PN, 2PN, and (E)-2M2BN, dinitriles,such as ADN and MGN, catalyst, catalyst degradation products andpromoter, may be contacted with a non-polar hydrocarbon extractionsolvent in an extraction zone according to a method described in U.S.Pat. Nos. 3,773,809 and 6,936,171. An extract stream including catalystand extraction solvent and a raffinate stream including extractionsolvent, pentenenitriles, dinitriles, catalyst degradation products, andpromoter are withdrawn from the extraction zone. The extract stream maybe charged to a distillation apparatus.

The extract stream is distilled to obtain a first extractionsolvent-enriched stream and a catalyst-enriched stream including therecovered catalyst. The catalyst-enriched stream including nickelcomplexes of the phosphorus-containing ligand may be recycled to contact3PN and HC≡N in the presence of the promoter to produce ADN.

The raffinate stream may be distilled in one or more distillationcolumns to obtain a second extraction solvent-enriched stream, apentenenitrile-enriched stream including 3PN, a dinitrile-enrichedstream, a dinitrile-depleted stream including the catalyst degradationproducts and promoter, a MGN-enriched stream, and a MGN-depleted streamincluding the recovered ADN.

Extraction solvent from the first and second extraction solvent-enrichedstreams may be reused in the extraction zone. Pentenenitrile from thepentenenitrile-enriched stream may be used as a solvent source forpreparing the first, second or third catalyst. 3PN may also be separatedfrom the pentenenitrile-enriched stream and may contact catalyst andHC≡N in the presence of the promoter to produce ADN, provided that the3PN is sufficiently free of C₈H₁₃C≡N compounds or compounds, such asphenol or cresols, which are capable of reacting with thephosphorus-containing ligand used in the catalyst for reacting 3PN withHC≡N.

The extract stream may be distilled in at least one distillation columnat 1 psia to 22 psia (0.07 bar to 1.5 bar) pressure and with a basetemperature of less than about 150° C., for example, less than about140° C., for example, less than about 130° C., or, for example, lessthan about 120° C. The base temperature is chosen in part to maintainthe thermal stability of the catalyst composition.

Distillation of the raffinate phase is shown in FIG. 3, as describedabove.

Although a majority of the extraction solvent separates into the solventphase in the extraction zone, some extraction solvent is extracted intothe raffinate phase, which is delivered to distillation column K′₁ inFIG. 3 through line 600. The raffinate stream, therefore, comprises someextraction solvent. The raffinate stream 600 may further comprise one ormore of at least one pentenenitrile (typically a mixture ofpentenenitriles), intermediate boilers and dinitriles comprisingadiponitrile (ADN) and methylglutaronitrile (MGN). In a firstdistillation step of the raffinate stream, extraction solvent (in FIG.3, withdrawn through stream 625) having a lower boiling point thanpentenenitriles may be separated from other higher boiling constituentsof the raffinate stream to obtain an extraction solvent depletedraffinate stream, which is withdrawn from column K′₁ through line 620.The extraction solvent withdrawn through line 625 may have a boilingpoint of, for example, from 30 to 135° C., for example, from 60 to 100°C. An example of such an extraction solvent is cyclohexane, which has aboiling point (BP) of 81° C.

In a second distillation step of the raffinate stream, pentenenitrilemay be removed from other higher boiling components of the raffinatestream to obtain a pentenenitrile-depleted raffinate stream. In FIG. 3,this pentenenitrile-depleted raffinate stream 630 is obtained bydistilling an extraction solvent depleted stream 620 in distillationcolumn K′₂. This pentenenitrile-depleted raffinate stream 630 maycomprise, for example, a total of at least 0.01% by weight ofpentenenitrile including the sum of 4-pentenenitrile, 3-pentenenitrile,and 2-pentenenitrile. Examples of pentenenitriles, which may be removedas an overhead stream 650 in this second distillation step include2-methyl-3-butenenitrile, trans-3-pentenenitrile, cis-3-pentenenitrile,trans-2-pentenenitrile, and cis-2-pentenenitrile. Thispentenenitrile-depleted raffinate stream may comprise, for example, atotal of at least 0.01%, for example, 0.07%, for example 0.1%, forexample, less than 1%, by weight of pentenenitrile including the sum of4-pentenenitrile, 3-pentenenitrile, and 2-pentenenitrile. Such removedpentenenitriles may have an approximate boiling point within the rangeof from 120° C. to 150° C.

The pentenenitrile-depleted raffinate stream 630 obtained in theabove-mentioned second distillation step may be introduced into at leasta third distillation step. In FIG. 3, this third distillation step takesplace in column K′₃. In this third distillation step, compositionshaving a higher boiling point than dinitriles are separated as a bottomstream 640 from dinitriles and any coboilers present, such asintermediate boilers. Such bottoms products in stream 640 may have aboiling point of, for example, at least 300° C. In contrast, mostdinitriles in the pentenenitrile-depleted raffinate stream 630 from theabove-mentioned second distillation step would tend to have a boilingpoint within the approximate range of 260° C. to 300° C. Thesedinitriles and intermediate boilers tend to be withdrawn as an overheaddraw through stream 635.

In FIG. 3, stream 635 may then be passed to distillation column K′₄ toproduce adiponitrile as a bottoms stream 660 and an overhead stream 670comprising MGN and intermediate boilers.

Stream 640 comprising catalyst degradation products from column K′₃ maybe passed to a wiped film evaporator (WFE) to recover adiponitrile insuch bottoms. One or more streams comprising catalyst degradationbyproducts from column K₃ in FIG. 2 may also, optionally, be passed tothis wiped film evaporator.

Although particular distillation steps are described above forconverting the raffinate stream from the extraction zone into a purifiedadiponitrile stream, it will be understood that other distillation stepsare possible. It is within the ordinary skill in the art to design andoperate such steps. Streams of compounds removed from the adiponitrilein the raffinate may be disposed of, further refined, used in adifferent reaction process or recycled to an appropriate point in theoverall reaction system.

Yield of and Purity of Adiponitrile (ADN)

The adiponitrile chemical yield from 1,3-butadiene may be greater than60%, for example, greater than 85% or greater than 90%, and theadiponitrile chemical yield from hydrogen cyanide may be greater than60%, for example, greater than 85% or greater than 90%.

By limiting the amount of C₉ mononitriles entering into the thirdreaction zone (Z₃), the amount of dinitriles of the formula C₈H₁₄(C≡N)₂,produced in the third reaction zone may be limited. For example, thereaction product from the third (Z₃) reaction zone may comprisesubstantially a dinitrile product comprising adiponitrile (ADN) andhaving less than 5000 parts per million (ppm); preferably less than 2000parts per million (ppm); most preferably less 500 parts per million(ppm) dinitriles (DDN) of chemical formula C₈H₁₄(C≡N)₂.

Optional Shared Catalyst Regeneration Zone

The zones described herein where catalyst is partially purified byremoval of catalyst degradation products and reaction byproducts arereferred to herein as purification zones or regeneration zones. When thephosphorus-containing ligands of the first and second catalysts areidentical, the first and second catalyst regeneration zones may becombined (co-mingled) as a shared catalyst regeneration zone comprisingliquid-liquid extraction. This option further comprises feeding at leasta portion of the first catalyst from the first catalyst purge, feedingat least a portion of the second catalyst from the second catalyst purgeor feeding a combination thereof to the shared catalyst regenerationzone to at least partially separate catalyst degradation product andreaction byproduct from a separated catalyst.

At least a portion of the separated catalyst from the shared catalystregeneration zone may be contacted with 1,3-butadiene and hydrogencyanide in the first reaction zone (Z₁) to produce the first reactioneffluent.

At least a portion of the separated catalyst from the shared catalystregeneration zone may be contacted with 2-methyl-3-butenenitrile in thesecond (Z₂) reaction zone to produce the second reaction effluent.

Catalyst from the shared catalyst regeneration zone may be contactedwith both 1,3-butadiene and hydrogen cyanide in the first reaction zone(Z₁) and with 2-methyl-3-butenenitrile in the second reaction zone (Z₂).

The optional shared catalyst regeneration zone for the first and secondcatalyst is generally not used when the ligands of the first and secondcatalysts are different.

The First, Second and Third Catalysts

As used herein, the term “catalyst” includes within its meaning acatalyst precursor composition. This meaning indicates that thezero-valent nickel at some point becomes bound to at least onephosphorus-containing ligand. Furthermore, additional reactions occurduring hydrocyanation, e.g., complexing of the initial catalystcomposition to an ethylenically unsaturated compound. As used herein,the term “catalyst” also includes within its meaning recycled catalyst,that is, a catalyst comprising a zero-valent nickel and at least onephosphorus-containing ligand which, having been used in the process ofthe invention, is returned or may be returned to the process and usedagain or used repeatedly. Suitable solvents for the catalysts includeextraction solvents useful in the process, for example, polar solventssuch as nitriles, for example, pentenenitriles such as 3-pentenenitrile,and non-polar solvents such as aliphatic hydrocarbons, for example,cyclohexane.

The first, second and third catalysts each comprise zero valent nickeland a phosphorus-containing ligand. These catalysts may be the same ordifferent. Optionally, the first, second and third catalysts are alldifferent. Optionally, the first and second catalysts are the same, andthe third catalyst is different. Optionally, the second and thirdcatalysts are the same, and the first catalyst is different. Optionally,the first and second catalysts comprise the same or differentmonodentate ligand, and the third catalyst comprises a bidentate ligand.Optionally, the first catalyst comprises a monodentate ligand, and thesecond catalyst and third catalysts comprise the same or differentbidentate ligand.

The chemical yield of adiponitrile may be increased from the reaction of1,3-butadiene and hydrogen cyanide over what can be achieved when thefirst catalyst, second catalyst, and the third catalyst are the samewith respect to the phosphorus-containing ligand and the same catalystflows into the first, second and third reaction zones.

The first catalyst for reacting BD with HC≡N may comprise, for example,zero-valent Ni and at least one monodentate phosphorus-containingligand. Also, the third catalyst for reacting 3PN with HC≡N may besegregated from the first (Z₁) and second (Z₂) reaction zones. Further,the steps for purifying the first and third catalysts are preferablysegregated, at least to the extent to avoid a mixture of the first andthird catalyst from being introduced into a reaction zone.

The third catalyst may be segregated from the first (Z₁) and second (Z₂)zones by not recycling the third catalyst back (either directly orindirectly) to the first (Z₁) and second (Z₂) reaction zones, or indeedto any location upstream of the second (Z₂) reaction zone or streamsthereto.

When the ligand of the first and second catalysts is a monodentateligand and the ligand of the third catalyst is a bidentate ligand, thethird catalyst may be segregated from the first and second reactionzone. By segregating the third catalyst from the first (Z₁) and second(Z₂) reaction zones, the concentration of the phosphorus-containingmultidentate ligand in the third catalyst in either the first or thesecond reaction zones may be no more than 100 ppm, for example, no morethan 50 ppm, for example, no more than 10 ppm, for example, no more than5 ppm, for example, no more than 1 ppm, and for example, substantiallyzero.

Although small amounts (e.g., traces) of the first catalyst may bepresent in the feed stream 300 to the third reaction zone (Z₃), thefirst catalyst is preferably not intentionally introduced to the third(Z₃) reaction zone. Thus, in a preferred embodiment, the purified streamof the first catalyst in line 156 from the distillation column 155 isrecycled to at least one of the first reaction zone (Z₁) via line 146and, optionally, to the second reaction zone (Z₂) via line 246, but noneof this stream in line 156 is passed to the third reaction zone (Z₃). Ingeneral, at least 90%, for example, at least 95%, for example, at least99%, for example, at least 99.9% and suitably, substantially all of thefirst catalyst recycled to at least one of the first reaction zone (Z₁)and the second reaction zone (Z₂), and/or less than 10%, for example,less than 5%, for example, less than 1%, for example, less than 0.1%,and suitably none of the first catalyst is introduced to the thirdreaction zone (Z₃).

Nevertheless, the present invention does tolerate some of the firstcatalyst passing downstream to the third reaction zone (Z₃), althoughthis is normally achieved by routes other than passing the purifiedstream of first catalyst in line 156 from the distillation column 155 tothe third reaction zone (Z₃), as will be appreciated from the processdescriptions herein. For example, some of the first catalyst mayunintentionally pass into the third reaction zone (Z₃) as a result of aunit upset or operator error without the need to shut down the entireintegrated process and remove first catalyst from the third reactionzone (Z₃).

When the ligand of the first catalyst is a monodentate ligand and theligand of the third catalyst is a bidentate ligand, the concentration ofthe phosphorus-containing monodentate ligand of the first catalyst inthe third reaction zone (Z₃) may be no more than 500 ppm, preferably nomore than 100 ppm, preferably no more than 50 ppm, preferably no morethan 10 ppm, preferably no more than 5 ppm, preferably no more than 1ppm, and preferably substantially zero.

The reaction of nickel metal with at least one freephosphorus-containing ligand is taught in U.S. Pat. Nos. 3,903,120,4,385,007, 4,416,825; United States Patent Application Publication No.20040176622, and PCT Patent Application Publication No. 1995011077,incorporated herein by reference.

Catalyst compositions comprising at least one phosphorus-containingligand may be substantially free and maintained separate from at leastone of carbon monoxide, oxygen, and water. These catalyst compositionsmay be preformed or prepared in situ according to techniques well knownin the art. For example, the catalyst composition may be formed bycontacting a monodentate or bidentate phosphite ligand with azero-valent nickel compound having ligands easily displaced byorganophosphite ligands, such as Ni(COD)₂, Ni[P(O-o-C₆H₄CH₃)₃]₃, andNi[P(O-o-C₆H₄CH₃)₃]₂(C₂H₄), all of which are well known in the art,wherein 1,5-cyclooctadiene (COD), tris(ortho-tolyl)phosphite[P(O-o-C₆H₄CH₃)₃], and ethylene (C₂H₄) are the easily displaced ligands,where the lower case “o” represents ortho. Elemental nickel, preferablynickel powder, when combined with a halogenated catalyst, as describedin U.S. Pat. No. 3,903,120; is also a suitable source of zero-valentnickel.

Alternatively, divalent nickel compounds can be combined with a reducingagent, to serve as a source of zero-valent nickel in the reaction, inthe presence of a monodentate or bidentate phosphite ligands. Suitabledivalent nickel compounds include compounds of the formula NiZ₂ where Zis halide, carboxylate, or acetylacetonate. Suitable reducing agentsinclude metal borohydrides, metal aluminum hydrides, metal alkyls, Li,Na, K, Zn, Fe or H₂ and electro-chemical means known from the art. See,for example, U.S. Pat. No. 6,893,996, which is incorporated herein byreference. In a catalyst composition, the bidentate phosphite ligand maybe present in excess of what can theoretically be coordinated to thenickel at a given time.

When a divalent nickel compound is reacted with a reducing agent, aLewis acid may be generated as a byproduct. For example, when NiCl₂ isreacted with zero valent Zn in the presence of a ligand, there is formeda catalyst comprising zero valent Ni and ZnCl₂, which is a Lewis acid.It is possible to use such a reaction product as a feed of both catalystand Lewis acid to the third reaction zone (Z₃). However, this reactionproduct should be subjected to an appropriate purification step toremove Lewis acid before the catalyst is used as a feed to the firstreaction zone (Z₁). Such a purification step may involve liquid/liquidextraction and distillation. It is preferred to use zero valent Ni,instead of divalent Ni, as the nickel source for the first catalyst.

Suitable methods for preparing catalysts, which may be used as thefirst, second or third catalyst, are described in InternationalApplication Number PCT/US10/60381, International Application NumberPCT/US10/60388, INVISTA Attorney Docket Number PI2440 and INVISTAAttorney Docket Number PI2775.

The catalyst composition may be dissolved in a solvent non-reactivetoward, and miscible with, the hydrocyanation reaction mixture. Suitablesolvents include, for example, aliphatic and aromatic hydrocarbons with1 to 10 carbon atoms, and nitrile solvents such as acetonitrile.Alternatively, 3PN, a mixture of isomeric pentenenitriles, a mixture ofisomeric methylbutenenitriles, a mixture of isomeric pentenenitriles andisomeric methylbutenenitriles, or the reaction product from a previousreaction campaign, may be used to dissolve the catalyst composition.

As discussed herein above, catalyst may be regenerated by liquid/liquidextraction followed by distillation to remove extraction solvent. Theconcentration of nickel complexes in the catalyst, recovered in thisdistillation step, may be increased prior to contacting at least aportion of the concentrated nickel complexes, comprising zero-valentnickel and at least one phosphorus-containing ligand, with 1,3-butadieneand hydrogen cyanide in the first (Z₁) reaction zone to produce thefirst reaction effluent; and with 2-methyl-3-butenenitrile in the second(Z₂) reaction zone to produce the second reaction effluent; or theircombination. The concentration of nickel complexes may be increased bycontacting at least a portion of the extraction solvent-depleted streamwith nickel metal in an organonitrile solvent.

Phosphorus-Containing Ligand

The catalysts used in the process of the invention include zero-valentnickel and at least one phosphorus-containing (P-containing) ligand,such as a phosphite, a phosphonite, a phosphinite, a phosphine, and amixed P-containing ligand or a combination of such members.

The P-containing ligands chemically bond to nickel as complexescomprising zero-valent nickel, and the free P-containing ligands notbonded to the complexes, may be monodentate or multidentate, forexample, bidentate or tridentate. The term “bidentate” is well known inthe art and means both phosphorus atoms of the ligand may be bonded to asingle metal atom. The term “tridentate” means the three phosphorusatoms on the ligand may be bonded to a single metal atom. The terms“bidentate” and “tridentate” are also known in the art as chelateligands.

As used herein, the term “mixed P-containing ligand” means aP-containing ligand comprising at least one combination selected fromthe group consisting of a phosphite-phosphonite, aphosphite-phosphinite, a phosphite-phosphine, a phosphonite-phosphinite,a phosphonite-phosphine, and a phosphinite-phosphine or a combination ofsuch members.

At least one of the catalysts selected from the group of the firstcatalyst, the second catalyst, and the third catalyst may be differentwith respect to at least one phosphorus-containing ligand.

Suitable phosphorus-containing ligands for the first catalyst areselected from the group consisting of compounds of Formula I, FormulaIII, Formula IV, Formula IVa or combinations thereof. Suitablephosphorus-containing ligands for the second catalyst, are selected fromthe group consisting of compounds of Formula I, Formula III, Formula IV,Formula IVa or combinations thereof. Suitable phosphorous-containingligands for the third catalyst are selected from the group consisting ofcompounds of Formula I, Formula III, Formula IV, Formula IVa orcombinations thereof. Formula III has the structure,

wherein,

-   -   X¹¹, X¹², X¹³, X²¹, X²², X²³ independently represent oxygen or a        single bond;    -   R¹¹, R¹² independently represent identical or different, single        or bridged organic radicals;

R²¹, R²² independently represent identical or different, single orbridged organic radicals; and

-   -   Y represents a bridging group.

In a preferred embodiment, X¹¹, X¹², X¹³, X²¹, X²², X²³ may each beoxygen. In such a case, the bridging group Y is bonded to phosphitegroups. In another preferred embodiment, X¹¹ and X¹² may each be oxygenand X¹³ a single bond, or X¹¹ and X¹³ each oxygen and X¹² a single bond,so that the phosphorus atom surrounded by X¹¹, X¹² and X¹³ is thecentral atom of a phosphonite. In such a case, X²¹, X²² and X²³ may eachbe oxygen, or X²¹ and X²² may each be oxygen and X²³ a single bond, orX²¹ and X²³ may each be oxygen and X²² a single bond, or X²³ may beoxygen and X²¹ and X²² each a single bond, or X²¹ may be oxygen and X²²and X²³ each a single bond, or X²¹, X²² and X²³ may each be a singlebond, so that the phosphorus atom surrounded by X²¹, X²² and X²³ may bethe central atom of a phosphite, phosphonite, phosphinite or phosphine,preferably a phosphonite. In another preferred embodiment, X¹³ may beoxygen and X¹¹ and X¹² each a single bond, or X¹¹ may be oxygen and X¹²and X¹³ each a single bond, so that the phosphorus atom surrounded byX¹¹, X¹² and X¹³ is the central atom of a phosphonite. In such a case,X²¹, X²² and X²³ may each be oxygen, or X²³ may be oxygen and X²¹ andX²² each a single bond, or X²¹ may be oxygen and X²² and X²³ each asingle bond, or X²¹, X²² and X²³ may each be a single bond, so that thephosphorus atom surrounded by X²¹, X²² and X²³ may be the central atomof a phosphite, phosphinite or phosphine, preferably a phosphinite. Inanother preferred embodiment, X¹¹, X¹² and X¹³ may each be a singlebond, so that the phosphorus atom surrounded by X¹¹, X¹² and X¹³ is thecentral atom of a phosphine. In such a case, X²¹, X²² and X²³ may eachbe oxygen, or X²¹, X²² and X²³ may each be a single bond, so that thephosphorus atom surrounded by X²¹, X²² and X²³ may be the central atomof a phosphite or phosphine, preferably a phosphine. The bridging groupY is preferably an aryl group which is substituted, for example byC₁-C₄-alkyl, halogen, such as fluorine, chlorine, bromine, halogenatedalkyl, such as trifluoromethyl, aryl, such as phenyl, or isunsubstituted, preferably a group having from 6 to 20 carbon atoms inthe aromatic system, in particular pyrocatechol, bis(phenol) orbis(naphthol). The R¹¹ and R¹² radicals may each independently beidentical or different organic radicals. Advantageous R¹¹ and R¹²radicals are aryl radicals, preferably those having from 6 to 10 carbonatoms, which may be unsubstituted or mono- or polysubstituted, inparticular by C₁-C₄-alkyl, halogen, such as fluorine, chlorine, bromine,halogenated alkyl, such as trifluoromethyl, aryl, such as phenyl, orunsubstituted aryl groups. The R²¹ and R²² radicals may eachindependently be identical or different organic radicals. AdvantageousR²¹ and R²² radicals are aryl radicals, preferably those having from 6to 10 carbon atoms, which may be unsubstituted or mono- orpolysubstituted, in particular by C₁-C₄-alkyl, halogen, such asfluorine, chlorine, bromine, halogenated alkyl, such as trifluoromethyl,aryl, such as phenyl, or unsubstituted aryl groups. The R¹¹ and R¹²radicals may each be separate or bridged. The R²¹ and R²² radicals mayalso each be separate or bridged. The R¹¹, R¹², R²¹ and R²² radicals mayeach be separate, two may be bridged and two separate, or all four maybe bridged, in the manner described.

Formula IV has the structure,P(X¹R¹)(X²R²)(X³R³)  Formula IV

wherein,

-   -   X¹, X², X³ independently represent oxygen or a single bond; and    -   R¹, R² and R³ are each independently identical or different        organic radicals. R¹, R² and R³ are each independently alkyl        radicals preferably having from 1 to 10 carbon atoms, such as        methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl,        t-butyl, aryl groups such as phenyl, o-tolyl, m-tolyl, p-tolyl,        1-naphthyl, 2-naphthyl, or hydrocarbyl, preferably having from 1        to 20 carbon atoms, such as 1,1′-biphenol, 1,1′-binaphthol. The        R¹, R² and R³ groups may be bonded together directly, i.e. not        solely via the central phosphorus atom. Preference is given to        the R¹, R² and R³ groups not being bonded together directly. In        a preferred embodiment, R¹, R² and R³ groups are radicals        selected from the group consisting of phenyl, o-tolyl, m-tolyl        and p-tolyl. In a particularly preferred embodiment, a maximum        of two of the R¹, R² and R³ groups should be phenyl groups. In        another preferred embodiment, a maximum of two of the R¹, R² and        R³ groups should be o-tolyl groups. Particularly preferred        compounds which may be used are those of the formula (IVa)        below:        (o-tolyl-O-)_(w)(m-tolyl-O-)_(x)(p-tolyl-O-)_(y)(phenyl-O—)_(z)P  Formula        (IVa)    -   where w, x, y, z are each a natural number and the following        conditions apply: w+x+y+z=3 and w, z<=2.

Examples of such compounds (IIa) are (o-tolyl-O—)₃P,(p-tolyl-O-)(phenyl-O—)₂P, (m-tolyl-O—) (phenyl-O—)₂P,(o-tolyl-O-)(phenyl-O—)₂P, (p-tolyl-O-)₂(phenyl-O—)P,(m-tolyl-O-)₂(phenyl-O—)P, (o-tolyl-O-)₂(phenyl-O—)P,(m-tolyl-O-)(p-tolyl-O-)(phenyl-O—)P,(o-tolyl-O-)(p-tolyl-O-)(phenyl-O—)P,(o-tolyl-O-)(m-tolyl-O-)(phenyl-O—)P, (p-tolyl-O—)₃P,(m-tolyl-O-)(p-tolyl-O—)₂P, (o-tolyl-O-)(p-tolyl-O—)₂P,(m-tolyl-O-)₂(p-tolyl-O—)P, (o-tolyl-O-)₂(p-tolyl-O—)P,(o-tolyl-O-)(m-tolyl-O-)(p-tolyl-O—)P, (m-tolyl-O—)₃P,(o-tolyl-O-)(m-tolyl-O—)₂P, (o-tolyl-O-)₂(m-tolyl-O—)P or mixtures ofsuch compounds.

An example of a bidentate phosphite ligand that is useful in the presentprocess is that having the Formula V, shown below

Further examples of bidentate phosphite ligands that are useful in thepresent process include those having the Formulae VI to IX, shown belowwherein for each formula, R¹⁷ is selected from the group consisting ofmethyl, ethyl or iso-propyl, and R¹⁸ and R¹⁹ are independently selectedfrom H or methyl:

Additional examples of bidentate phosphite ligands that are useful inthe present process include a ligand selected from a member of the grouprepresented by Formulae X and XI, in which all like reference charactershave the same meaning, except as further explicitly limited:

wherein,

-   -   R⁴¹ and R⁴⁵ are independently selected from the group consisting        of C₁ to C₅ hydrocarbyl, and each of R⁴², R⁴³, R⁴⁴, R⁴⁶, R⁴⁷ and        R⁴⁸ is independently selected from the group consisting of H and        C₁ to C₄ hydrocarbyl.

For example, the bidentate phosphite ligand can be selected from amember of the group represented by Formula X and Formula XI, wherein

-   -   R⁴¹ is methyl, ethyl, isopropyl or cyclopentyl;    -   R⁴² is H or methyl;    -   R⁴³ is H or a C₁ to C₄ hydrocarbyl;    -   R⁴⁴ is H or methyl;    -   R⁴⁵ is methyl, ethyl or isopropyl; and    -   R⁴⁶, R⁴⁷ and R⁴⁸ are independently selected from the group        consisting of H and C₁ to C₄ hydrocarbyl.

As additional examples, the bidentate phosphite ligand can be selectedfrom a member of the group represented by Formula X, wherein

-   -   R⁴¹, R⁴⁴, and R⁴⁵ are methyl;    -   R⁴², R⁴⁶, R⁴⁷ and R⁴⁸ are H; and    -   R⁴³ is a C₁ to C₄ hydrocarbyl;    -   or    -   R⁴¹ is isopropyl;    -   R⁴² is H;    -   R⁴³ is a C₁ to C₄ hydrocarbyl;    -   R⁴⁴ is H or methyl;    -   R⁴⁵ is methyl or ethyl;    -   R⁴⁶ and R⁴⁸ are H or methyl; and    -   R⁴⁷ is H, methyl or tertiary-butyl;        or the bidentate phosphite ligand can be selected from a member        of the group represented by Formula XI, wherein    -   R⁴¹ is isopropyl or cyclopentyl;    -   R⁴⁵ is methyl or isopropyl; and    -   R⁴⁶, R⁴⁷, and R⁴⁸ are H.

As yet another example, the bidentate phosphite ligand can berepresented by Formula X, wherein R⁴¹ is isopropyl; R⁴², R⁴⁶, and R⁴⁸are H; and R⁴³, R⁴⁴, R⁴⁵, and R⁴⁷ are methyl.

It will be recognized that Formulae V to XI are two-dimensionalrepresentations of three-dimensional molecules and that rotation aboutchemical bonds can occur in the molecules to give configurationsdiffering from those shown. For example, rotation about thecarbon-carbon bond between the 2- and 2′-positions of the biphenyl,octahydrobinaphthyl, and or binaphthyl bridging groups of Formulae V toXI, respectively, can bring the two phosphorus atoms of each Formula incloser proximity to one another and can allow the phosphite ligand tobind to nickel in a bidentate fashion. The term “bidentate” is wellknown in the art and means both phosphorus atoms of the ligand arebonded to a single nickel atom.

At least one phosphorus-containing ligand for the first catalyst may be,for example, selected from the group consisting of compounds of FormulaIV, wherein Formula IV has the structure above.

At least one phosphorus-containing ligand for the second catalyst maybe, for example, selected from the group consisting of compounds ofFormulae III and IV, wherein Formulae III and IV have the structureabove.

At least one phosphorus-containing ligand for the third catalyst may beselected from the group consisting of compounds of Formula III, whereinFormula III has the structure above.

Lewis Acid Promoter

The reaction, which takes place in the third reaction zone (Z₃) forhydrocyanating 3-pentenenitrile to produce adiponitrile, preferablytakes place in the presence of a promoter for promoting this reaction.The promoter may be a Lewis acid, such as an inorganic compound, anorganometallic compound, or combinations thereof, in which a cation ofthe Lewis acid is selected from the group consisting of scandium,titanium, vanadium, chromium, manganese, iron, cobalt, copper, zinc,boron, aluminum, yttrium, zirconium, niobium, molybdenum, cadmium,rhenium, lanthanum, erbium, ytterbium, samarium, tantalum, and tin.However, the reactions, which take place in the first reaction zone (Z₁)for hydrocyanating 1,3-butadiene and the second reaction zone (Z₂) forisomerizing 2-methyl-3-butenenitrile, preferably take place in theabsence or substantial absence of such a promoter. It will be understoodthat the expression, substantial absence, allows for some measurablepromoter to be present, provided that the amount of the promoter is notsufficient to significantly impact the selectivity or yield of thereactions taking place in the first reaction zone (Z₁) and the secondreaction zone (Z₂).

Dinitriles may be produced in the first reaction zone by the reaction of3PN or 2M3BN with HCN. Lewis acids are capable of promoting theformation of dinitriles in the first reaction zone. Lewis acids arepreferably not introduced into the first reaction zone in detectableamounts. However, a detectable amount of a Lewis acid may be introducedinto the first reaction zone, provided that dinitrile formation isminimized. For example, a detectable amount of a Lewis acid may beintroduced into the first reaction zone, provided that the amount ofdinitriles produced, when none of the Lewis acid is introduced into thefirst reaction zone, is not increased by more than 5 wt %.

Lewis acid may be unintentionally introduced into the first reactionzone as a result of a unit upset or operator error. However, thecontinuous production of 3-pentenenitrile may be maintained, providedthat the ratio of atomic equivalents of Ni to moles of Lewis Acid in thefirst reaction zone is less than 10:1 during the course of at least 95%of the production of 3-pentenenitrile.

3-pentenenitrile produced in the first and second reaction zones may bereacted with hydrogen cyanide to produce dinitriles comprisingadiponitrile in a third reaction zone downstream of the first and secondreaction zones. A catalyst and a Lewis acid promoter may flow throughthe third reaction zone along with reactants and products. Preferably,none of the Lewis acid promoter which flows from the third reaction zoneflows into the first reaction zone. However, it is possible that aportion of the Lewis acid promoter which flows from the third reactionzone flows into the first reaction zone, provided that the unwantedproduction of dinitriles in the first reaction is minimized, asdiscussed above.

Distillation Equipment

Distillation steps described herein may be performed in any suitableequipment known to one skilled in the art. Examples of conventionalequipment suitable for this distillation include sieve tray columns,bubble tray columns, columns with regular packing, random packed columnsor single-stage evaporators, such as falling film evaporators, thin-filmevaporators, flash distillation evaporators, multi-phase helical coilevaporators, natural circulation evaporators or forced circulation flashevaporators. The distillation can be performed in one or more pieces ofequipment.

Distillation equipment comprise at least one distillation column. Adistillation column may be provided with a structured packing sectionabove the feed location to prevent catalyst entrainment in thedistillate and to generate an appropriate separation.

The examples which follow demonstrate the present invention and itscapability for use. These examples are regarded as illustrative innature and not restrictive.

Example 1 Shared Catalyst Recovery System and Bidentate Ligand inReaction Zones Z₁, Z₂ and Z₃

This Example 1 describes operation of a two-step process for thehydrocyanation of 1,3-butadiene to make adiponitrile using a single,shared catalyst purification system for each of the first reaction zonefor hydrocyanating 1,3-butadiene, (Z₁), the second reaction zone forisomerizing mixed pentenenitriles to enrich the mixture in3-pentenenitrile (Z₂) and the third reaction zone for hydrocyanating3-pentenenitrile to adiponitrile (Z₃). These Examples use the term“catalyst loop” to include the identified reaction zone (Z₁, Z₂ or Z₃)along with its associated catalyst handling equipment that may includeprocess equipment for separating, purifying and recycling the catalyst,as well as adding fresh make-up catalyst.

1,3-butadiene and hydrogen cyanide are charged to a first reaction zone(Z₁), as shown in FIG. 1, where the mixture is contacted in the presenceof a first catalyst comprising zero-valent Ni and a phosphite-containingligand, collectively a catalyst system, to produce a reaction productsubstantially comprising 3-pentenenitrile (3PN) and2-methyl-3-butenenitrile (2M3BN). In this Example 1, the catalyst systemcomprises a bidentate phosphite ligand of Formula III as disclosedherein.

As shown in FIG. 1, 1,3-butadiene reactant is fed into the firstreaction zone (Z₁) through line 100, hydrogen cyanide reactant is fedinto the first reaction zone (Z₁) through line 120, and catalyst is fedinto the first reaction zone (Z₁) through line 140. A reaction productstream is taken from the first reaction zone (Z₁) through line 122. Thereaction product stream in line 122 comprises products, byproducts,unreacted reactants and catalyst, which flows through the first reactionzone (Z₁). The reaction product stream 122 is introduced into aseparation section 125, to obtain, inter alia, a concentrated catalyststream 140 and product stream 200 comprising 2-methyl-3-butenenitrile(2M3BN). The separation section 125 comprises one or more distillationcolumns as shown in FIG. 4. Unreacted hydrogen cyanide and 1,3-butadienemay also be separated from reaction products and catalyst in separationsection 125, although HCN is usually reacted to extinction during normalunit operation. Unreacted 1,3-butadiene is recycled to the firstreaction zone (Z₁) through lines not shown in FIG. 1. A streamcomprising 3-pentenenitrile (3PN) is also withdrawn from separationsection 125 through a line not shown in FIG. 1. At least a portion ofthe catalyst separated from reaction products in separation section 125is recycled to the first reaction zone (Z₁) through line 140.

Subsequent to the reaction in the first reaction zone (Z₁), thesubstantial isomerization of 2M3BN in a second reaction zone (Z₂) isconducted in the presence of an isomerization catalyst to producereaction product comprising substantially 3PN. In this Example 1, theisomerization catalyst is the same catalyst composition introduced intothe first reaction zone (Z₁).

As shown in FIG. 1, a feed comprising 2M3BN is introduced into thesecond reaction zone (Z₂) through line 200. Catalyst is introduced intothe second reaction zone (Z₂) through line 240. The effluent stream 222from the second reaction zone (Z₂) comprises catalyst and 3PN product.This effluent stream 222 passes into separation section 225 to obtain,inter alia, a 3PN product stream 300 and a concentrated catalyst stream240. Separation section 225 comprises a series of distillation columnsas shown in FIG. 5.

Catalyst recycle systems are shown in FIG. 1 for supplying catalyst tothe first reaction zone (Z₁), the second reaction zone (Z₂) and thethird reaction zone (Z₃). In this Example, the catalyst recycle systemsare different from those shown in FIG. 1. In particular, all threereaction zones in this Example 1 share a single catalyst purificationand regeneration system.

In the catalyst recycle system for supplying catalyst to the firstreaction zone (Z₁), a portion of the concentrated catalyst stream inline 140 is diverted into catalyst purge stream 126. This catalyst purgestream 126 is mixed with stream 226 and charged, along with stream 400,to extraction zone 370. The regenerated catalyst stream 340 then returnsto Z₁ and Z₂ as streams 140 and 240, respectively.

In this Example 1, the first reaction zone (Z₁) and second reaction zone(Z₂) are not provided with dedicated, isolated catalyst recoverysystems. They share the catalyst recovery system as described above forthe third reaction zone (Z₃). Catalyst purge streams from the firstreaction zone (Z₁) and the second reaction zone (Z₂) are combined andcharged to extraction zone 370 as shown in FIG. 1.

In this Example 1, Lewis acid from the third reaction zone (Z₃) carriesover to reaction zones Z₁ and Z₂ with recycled catalyst into the sharedliquid-liquid extraction zone 370 and the catalyst purification andrecovery steps.

Example 1 Operating Parameters and Results

Nickel dosage is maintained at about 500 ppm weight (based on totalfeed) in the first reaction zone (Z₁). Ligand dosage is controlled ataround 3:1 molar ratio of bidentate ligand:nickel.

Catalyst loss is observed when the bottoms (process side of thereboiler) operating temperature in the butadiene column (the firstdistillation column after the first reaction zone) exceeds about 125° C.While not to limit the scope of the invention by a recitation of theory,it is believed that the loss of the bidentate ligand component of thecatalyst is due to thermal degradation. To maintain ligand inventory,the butadiene column bottoms (the first column after the first reactionzone) is controlled at 125° C. Initially, this results in anunacceptably high level of unreacted butadiene in thepentenenitrile-enriched bottoms product. In an attempt to solve thisproblem, the butadiene column is upgraded for vacuum operation, andrefrigeration equipment is installed for condensing the overheads.Additional monitoring equipment is installed to detect oxygen intrusionfrom the atmosphere and mitigate the risk of uncontrolled 1,3-butadienepolymerization in the presence of oxygen.

The process is carried out under continuous operating conditions, andthe residual Lewis acid concentration in the catalyst increases. Thephysical state of the Lewis acid in the catalyst does not appear to becritical, and may be present in the catalyst in solution or byentrainment. The presence of the Lewis acid appears to correlate withincreased conversion of 1,3-butadiene to MGN in the first reaction zone(Z₁). This initial conversion of 1,3-butadiene to MGN results in loss ofADN yield.

Example 2 Segregated Catalyst Recovery Systems

This Example 2 illustrates segregated catalyst recovery systems. Inparticular, this Example 2 illustrates a process using three separatecatalyst recovery systems where each of reaction zones Z₁, Z₂ and Z₃contain catalyst comprising nickel and a bidentate phosphite-containingligand having the structure of Formula III, above.

In this Example 2, as shown in FIG. 1, 1,3-butadiene reactant is fedinto the first reaction zone (Z₁) through line 100, hydrogen cyanidereactant is fed into the first reaction zone (Z₁) through line 120, andcatalyst is fed into the first reaction zone (Z₁) through line 140. Areaction product stream is taken from the first reaction zone (Z₁)through line 122. The reaction product stream in line 122 comprisesproducts, byproducts, unreacted reactants and catalyst, which flowsthrough the first reaction zone (Z₁). The reaction product stream 122 isintroduced into a separation section 125, to obtain, inter alia, aconcentrated catalyst stream 140 and product stream 200 comprising2-methyl-3-butenenitrile (2M3BN). The separation section 125 maycomprise one or more distillation columns. An example of separationsection 125 is shown in FIG. 4. Unreacted hydrogen cyanide and1,3-butadiene may also be separated from reaction products and catalystin separation section 125. Unreacted 1,3-butadiene may be recycled tothe first reaction zone (Z₁) through lines not shown in FIG. 1. A streamcomprising 3-pentenenitrile (3PN) may also be withdrawn from separationsection 125 through a line not shown in FIG. 1. At least a portion ofthe catalyst separated from reaction products in separation section 125may be recycled to the first reaction zone (Z₁) through line 140.

Subsequent to the reaction in the first reaction zone (Z₁), thesubstantial isomerization of 2M3BN in a second reaction zone (Z₂) isconducted in the presence of an isomerization catalyst to produce areaction product comprising substantially 3PN. The isomerizationcatalyst is also referred to herein as the second catalyst. Theisomerization catalyst may be the same as the catalyst introduced intothe first reaction zone (Z₁). Optionally, the isomerization catalyst maybe different from the catalyst introduced into the first reaction zone(Z₁).

As shown in FIG. 1, a feed comprising 2M3BN is introduced into thesecond reaction zone (Z₂) through line 200. Catalyst is introduced intothe second reaction zone (Z₂) through line 240. The effluent stream 222from the second reaction zone (Z₂) comprises catalyst and 3PN product.This effluent stream 222 passes into separation section 225 to obtain,inter alia, a 3PN product stream 300 and a concentrated catalyst stream240. Separation section 225 may comprise one or more distillationapparatus. FIG. 5 shows an example of such a separation section 225.

Catalyst recycle systems are shown in FIG. 1 for supplying catalyst tothe first reaction zone (Z₁) and the second reaction zone (Z₂). Thesecatalyst recycle systems comprise further systems for purifying at leasta portion of the catalyst prior to recycle.

In the catalyst recycle system for supplying catalyst to the firstreaction zone (Z₁), a portion of the concentrated catalyst stream inline 140 is diverted into catalyst purge stream 126.

Catalyst in purge stream 126 is in the form of a solution includingimpurities, such as reaction byproducts and catalyst degradationbyproducts. Catalyst in purge stream 126 is fed to liquid/liquidextraction zone 150 to at least partially purify or regenerate thecatalyst. The catalyst is purified or regenerated in that at least somebyproducts are removed from the catalyst solution.

A non-polar solvent, such as an alkane, is fed into the liquid/liquidextraction zone 150 through line 130. A polar solvent, which isimmiscible with the non-polar solvent, is also fed into theliquid/liquid extraction zone 150 through line 500. In extraction zone150, there is formed a non-polar phase comprising non-polar solvent andcatalyst and a polar phase (e.g., a raffinate) comprising polar solventand, for example, reaction byproducts and catalyst degradation products.The non-polar phase is taken from extraction zone 150 via line 134 todistillation apparatus 155. The polar phase is taken from extractionzone 150 via line 510 to separation section 1000.

An example of separation section 1000 is described in greater detail inFIG. 2. Separation section 1000 may include, collectively, a series ofcolumns (K₁, K₂, K₃ and K₄) which provide for the removal of certainreaction byproducts and certain catalyst degradation products from thepolar solvent. The column bottom of K₄ provides polar solvent, which isreturned to extraction zone 150, via line 500.

Non-polar solvent is distillatively recovered in distillation apparatus155 and returned to extraction zone 150, via line 130. Extraction zone150, line 134, distillation apparatus 155 and line 130, collectively,form a recovery loop for recycling non-polar solvent into extractionzone 150. Extraction zone 150, line 510, separation section 1000 andline 500, collectively, form a recovery loop for recycling polar solventinto extraction zone 150. Additional non-polar solvent and polar solventmay be introduced into extraction zone 150 by lines not shown in FIG. 1.This additional solvent may be added for start up and for make-up ofsolvent lost during the course of the liquid/liquid extraction step.

Column bottoms from distillation column 155 include partially purifiedcatalyst. This catalyst is partially purified or regenerated in thesense that at least some of the catalyst degradation products and/orreaction byproducts have been separated from the solution containing thecatalyst. This partially purified catalyst may be taken fromdistillation column 155 through line 156 and introduced at any point forrecycle into the first reaction zone (Z₁). In FIG. 1, partially purifiedcatalyst may be taken from distillation column 155 through line 156 andtransferred into line 146 for introduction into catalyst recycle line140 for recycle into the first reaction zone (Z₁). FIG. 1 shows theintroduction of stream 146 downstream of the take-off stream 126, butthis stream may, optionally, be introduced upstream of the take-offstream 126. Stream 146 may also, optionally, be added to anycatalyst-containing stream associated with the first reaction zone (Z₁).

The partially purified stream of first catalyst, which is subsequentlyreturned to the first reaction zone (Z₁) may be provided with additionalzero-valent Ni and/or additional phosphorus-containing ligand. In FIG.1, additional zero-valent Ni and/or additional phosphorus-containingligand may be provided via line 145. Also as shown in FIG. 1, partiallypurified stream of first catalyst, which is subsequently fed to thefirst reaction zone (Z₁), may be provided with additional zero-valent Niand/or phosphorus-containing ligand via line 145. However, it will beunderstood, that make-up catalyst may be added via different routes, notshown in FIG. 1. For example, make-up catalyst stream 145 may be chargedto other sections of the first reaction zone catalyst loop or, forexample, directly to the first reaction zone (Z₁).

In this Example 2, the second reaction zone (Z₂) is provided with asecond catalyst recovery system for supplying catalyst to the secondreaction zone (Z₂). In this second catalyst recycle system, a portion ofthe concentrated catalyst stream in line 240 is diverted into catalystpurge stream 226. This catalyst purge stream 226 is fed intoliquid/liquid extraction zone 250. A non-polar solvent, such as analkane, is fed into the liquid/liquid extraction zone 250 through line230. A polar solvent, which is immiscible with the non-polar solvent, isalso fed into the liquid/liquid extraction zone 250 through line 700.Dinitriles from sources not shown in FIG. 1 may be added to extractionzone 250, as needed to accomplish desired phase separation andextraction. For example, a portion of the refined dinitrile productstream from the third reaction zone (Z₃) may be used. For example, aside stream (not shown) may be taken from line 500 and introduced intoextraction zone 250. In extraction zone 250, there is formed a non-polarphase comprising non-polar solvent and catalyst and a polar phase (e.g.,a raffinate) comprising, for example, polar solvent, reaction byproductsand certain catalyst degradation products. The non-polar phase is takenfrom extraction zone 250 via line 234 to distillation apparatus 255. Thepolar phase is taken from extraction zone 250 via line 710 to separationsection 2000. Separation section 2000 is described in greater detail inFIG. 2.

Separation section 2000 includes, collectively, a series of columns (K₁,K₂, K₃ and K₄) which provide for the separation of certain reactionby-products and catalyst degradation products. The column bottom of K₄provides polar solvent, which is returned to extraction zone 250, vialine 700. Additional polar solvent, in the form of adiponitrile, asneeded for phase separation, may be provided from adiponitrile producedin the third reaction zone (Z₃) through lines not shown in FIG. 1.

Non-polar solvent is distillatively recovered in distillation apparatus255 and returned to extraction zone 250, via line 230. Extraction zone250, line 234, distillation column 255 and line 230, collectively, forma recovery loop for recycling non-polar solvent into extraction zone250. Extraction zone 250, line 710, separation section 2000 and line700, collectively, form a recovery loop for recycling polar solvent intoextraction zone 250.

Column bottoms from distillation column 255 include partially purifiedcatalyst. This catalyst is partially purified or regenerated in thesense that at least some of the catalyst degradation products and/orreaction byproducts have been separated from the solution containing thecatalyst. This partially purified catalyst may be taken fromdistillation apparatus 255 through line 248 for introduction intocatalyst recycle line 240 for recycle into the second reaction zone(Z₂). Any partially purified stream of catalyst, which is subsequentlyfed to the second reaction zone (Z₂), may be provided with additionalzero-valent Ni and/or phosphorus-containing ligand, for example, vialine 245. Although not shown in FIG. 1, line 245 may optionally be feddirectly into line 246 or line 248 instead of line 240. Other ways ofintroducing make-up catalyst are known in the art and may be used.

The 3PN product in line 300 is introduced into the third reaction zone(Z₃), where 3PN is reacted with HCN. 3PN from separation section 125 mayalso be introduced into the third reaction zone (Z₃) through a line orlines not shown in FIG. 1. The HCN reactant feed is introduced into thethird reaction zone (Z₃) through line 220. The third catalystcomprising, optionally, zero-valent Ni and a bidentatephosphite-containing ligand, collectively a third catalyst system, and aLewis acid promoter is introduced into the third reaction zone (Z₃)through line 340. The reaction of 3PN and HCN in the third reaction zone(Z₃) produces a reaction product containing adiponitrile. A reactionproduct stream is taken from the third reaction zone (Z₃) by line 400.The reaction product stream comprises, for example, adiponitrile,catalyst, promoter, and unreacted reactants. The reaction product streammay optionally be passed through a separation section (not shown inFIG. 1) to remove unreacted reactants, prior to separation of catalystfrom adiponitrile product.

Catalyst and adiponitrile product from the product stream in line 400are passed into liquid/liquid extraction zone 370. A non-polar solvent,such as an alkane, is fed into the liquid/liquid extraction zone 370through line 330. The non-polar solvent introduced into theliquid/liquid extraction zone 370 may have the same or differentcomposition as the non-polar solvent introduced into the liquid/liquidextraction zone 150. Together, non-polar solvent from line 330 andadiponitrile product from line 400 comprise an extractant system ofimmiscible components. In extraction zone 370, there is formed anon-polar phase comprising non-polar solvent and catalyst and a polarphase (e.g., a raffinate) comprising adiponitrile, promoter and catalystdegradation products.

The non-polar phase is taken from extraction zone 370 via line 334 todistillation apparatus 375. The polar phase comprising adiponitrile istaken from extraction zone 370 via line 600 to adiponitrile purificationsection 3000. Adiponitrile purification section 3000 is described ingreater detail in FIG. 3.

Adiponitrile purification section 3000 may include, collectively, aseries of columns (K′₁, K′₂, K′₃ and K′₄) which provide for theseparation of impurities, such as reaction byproducts and catalystdegradation products. The column bottom of K′₄ provides the purifiedadiponitrile product, which is recovered in line 660. A portion of thepurified adiponitrile product may optionally be returned to extractionzone 150 or extraction zone 250 (by lines not shown in FIG. 1) tofacilitate phase separation in these extraction zones.

Non-polar solvent is distillatively recovered in distillation apparatus375 and returned to extraction zone 370, via line 330. Extraction zone370, line 334, distillation apparatus 375 and line 330, collectively,form a recovery loop for recycling non-polar solvent into extractionzone 370. Column bottoms from distillation column 375 include partiallypurified catalyst. This partially purified catalyst may be taken fromdistillation column 375 through line 340 for recycle of catalyst intothe third reaction zone (Z₃). The partially purified stream of thirdcatalyst in line 340, which is subsequently returned to the thirdreaction zone (Z₃), may be provided with make-up quantities ofadditional zero-valent Ni and/or third phosphorus-containing ligandalong with promoter. In FIG. 1, make-up quantities of additionalzero-valent Ni and/or third phosphorus-containing ligand and/or promotermay be added via line 345. However, it will be appreciated that thereare other ways of introducing make-up catalyst and promoter. Forexample, all or a portion of the recycled catalyst stream 340 may becharged to a catalyst reactor to increase its nickel content and theeffluent from the catalyst reactor may introduced at a suitable point.

FIG. 2 shows a distillation train, which may be used as separationsection 1000 or separation section 2000, shown in FIG. 1. In FIG. 2,line 515 represents either line 510 or line 710 of FIG. 1. Line 515transports a raffinate stream from either extraction zone 150 orextraction zone 250 into separation section 1000 or separation section2000, as shown in FIG. 1. The raffinate stream in line 515 is firstpassed into distillation column K₁, where extraction solvent isseparated from higher boiling components of the raffinate stream. Inparticular, extraction solvent, such as cyclohexane, is withdrawn fromdistillation column K₁ through line 525, and higher boiling componentsof the raffinate stream are withdrawn from distillation column K₁through line 520.

The solvent-depleted stream in line 520 is then passed into distillationcolumn K₂, where pentenenitrile is separated from higher boilingcomponents remaining in the raffinate stream. In particular,pentenenitrile, such as 3PN and 2M3BN, is withdrawn from distillationcolumn K₂ through line 550, and higher boiling components of theraffinate stream are withdrawn from distillation column K₂ through line530.

The pentenenitrile-depleted stream in line 530 is then passed intodistillation column K₃, where dinitriles are separated from higherboiling components remaining in the raffinate stream. In particular,dinitriles, such as ADN and MGN, are withdrawn from distillation columnK₃ through line 535, and higher boiling components of the raffinatestream are withdrawn from distillation column K₃ through line 540. Thesehigher boiling components in line 540 may comprise, for example,catalyst degradation products.

The dinitrile-enriched stream in line 535 is then passed intodistillation column K₄, where adiponitrile is separated from lowerboiling dinitriles, such as MGN. In particular, MGN is withdrawn fromdistillation column K₄ through line 420. The MGN-containing stream inline 420 also includes C₈H₁₃C≡N compounds and phenolic compounds. Anadiponitrile-enriched stream is withdrawn from distillation column K₄through line 560. In FIG. 2, line 560 represents either line 500 or line700 of FIG. 1. As shown in FIG. 1, the adiponitrile-enriched stream inline 500 is recycled to the liquid/liquid extraction zone 150, and theadiponitrile-enriched stream in line 700 is recycled to theliquid/liquid extraction zone 250.

FIG. 3 shows a distillation train, which may be used as adiponitrilepurification section 3000, shown in FIG. 1. Line 600 transports araffinate stream from extraction zone 370 into distillation column K′₁,where extraction solvent is separated from higher boiling components ofthe raffinate stream. In particular, extraction solvent, such ascyclohexane, is withdrawn from distillation column K′₁ through line 625,and higher boiling components of the raffinate stream are withdrawn fromdistillation column K′₁ through line 620.

The solvent-depleted stream in line 620 is then passed into distillationcolumn K′₂, where pentenenitrile is separated from higher boilingcomponents remaining in the raffinate stream. In particular,pentenenitrile, such as 3PN and 2M3BN, is withdrawn from distillationcolumn K′₂ through line 650, and higher boiling components of theraffinate stream are withdrawn from distillation column K′₂ through line630.

The pentenenitrile-depleted stream in line 630 is then passed intodistillation column K′₃, where dinitriles are separated from higherboiling components remaining in the raffinate stream. In particular,dinitriles, such as ADN and MGN, are withdrawn from distillation columnK′₃ through line 635, and higher boiling components of the raffinatestream are withdrawn from distillation column K′₄ through line 640.These higher boiling components in line 640 may comprise, for example,catalyst degradation products.

The dinitrile-enriched stream in line 635 is then passed intodistillation column K′₄, where adiponitrile is separated from lowerboiling dinitriles, such as MGN. In particular, an MGN-enriched streamis withdrawn from distillation column K′₄ through line 670, and apurified adiponitrile stream is withdrawn from distillation column K′₄through line 660.

FIG. 4 is a schematic representation of an example of a distillationtrain, which may be used as separation section 125, shown in FIG. 1.Stream 122 comprising 3PN, 2M3BN, at least one catalyst, and BD istransferred into an apparatus 810 for distillation. In this apparatus,stream 122 is distilled to obtain a BD-enriched stream 812 and aBD-depleted stream 813 comprising 3PN, 2M3BN, and at least one catalyst.The BD-enriched stream 812 may be recycled the first reaction zone (Z₁).

The BD-depleted stream 813, which comprises 3PN, 2M3BN, and at least onecatalyst is then transferred to another apparatus 820 for furtherdistillation. In this apparatus, stream 813 is distilled to obtain a topproduct stream 824 enriched in BD, a stream 825, comprising 3PN and2M3BN, and a bottom product stream 140 enriched in at least onecatalyst. Stream 824 enriched in BD may also be recycled to the firstreaction zone (Z₁). If excess dinitriles are present in, for example,apparatus 810 or 820, the catalyst may be less thermally stable, causingnickel to plate out on high-temperature surfaces such as exchanger tubesand reboiler walls. Alternatively, this may trigger precipitation ofnickel solids, for example, in the column bottoms. The presence ofexcess dinitriles may also limit the maximum operating temperature andrequire closer process control, especially temperature control.

Stream 825, comprising 3PN and 2M3BN, is transferred at least in part toanother distillation apparatus 830. In this apparatus, stream 825 isdistilled to obtain 2M3BN-enriched stream 200 and 2M3BN-depleted stream838 comprising 3PN. Stream 200 may be obtained at the top region of thedistillation apparatus, while the stream 838 may be obtained at thebottom region of the distillation apparatus.

FIG. 4 illustrates one distillation system for distilling the effluentfrom the first reaction zone (Z₁). However, it will be understood thatit is within the skill in the art to design and operate otherdistillation systems to achieve the same or essentially the sameresults. For example, depending upon the thermal stability of catalyst,it may be possible to combine distillation apparatus 810 anddistillation apparatus 820 into a single distillation apparatus, where aBN-enriched stream is withdraw as a top draw, a PN-enriched stream iswithdrawn as a side draw, and a catalyst-enriched stream is withdrawn asa bottom draw.

FIG. 5 is a schematic representation of an example of a distillationtrain, which may be used as separation section 225, shown in FIG. 1. Theisomerization reaction effluent in stream 222 obtained in the secondreaction zone is distilled to recover catalyst and products. Stream 222is introduced into distillation apparatus 940. A pentenenitrile-enrichedstream 942, comprising 3PN, 2M3BN, and (Z)-2M2BN, may be obtained fromthe distillation apparatus 940. Stream 942 may also comprise otherpentenenitriles, selected from 4PN, (E)-2M2BN, or a combination thereof,and optionally dimerized BD compounds having the empirical formulaC₈H₁₂, such as VCH and ethylidene cyclohexene isomers. Apentenenitrile-depleted stream 240, enriched in at least one catalyst,may be obtained as the bottom product.

Stream 942 may be distilled to purge at least a portion of thelower-boiling (Z)-2M2BN isomer from the 3PN and 2M3BN reaction productmixture.

Stream 942, comprising 3PN, 2M3BN, and (Z)-2M2BN, is distilled indistillation apparatus 950. Stream 954 is obtained as an overheadproduct that is enriched in (Z)-2M2BN. Stream 955, comprising 3PN and2M3BN, is obtained as a bottom product and is depleted in (Z)-2M2BN.“Enriched” and “depleted” in (Z)-2M2BN are relative to its concentrationin stream 942.

Stream 954 may also comprise other pentenenitriles, selected from thegroup comprising 2M3BN, (E)-2M2BN, and optionally dimerized BD compoundshaving the empirical formula C₈H₁₂, such as VCH and ethylidenecyclohexene isomers. Stream 955 may also comprise other pentenenitriles,selected from the group comprising 4PN, 2PN, and (E)-2M2BN.

The distillation is optionally operated in such a manner to causedimerized BD compounds to be enriched in stream 954 and depleted instream 955, both relative to the concentration of dimerized BD compoundsin stream 942. Optionally, dimerized BD compounds are enriched in stream954 through an azeotrope of said compounds with 2M3BN. As a result ofthe operations described above, stream 954 comprises greater than 1% byweight, for example greater than 5% by weight, for example greater than10% by weight of 2M3BN, relative to the total mass of stream 954.

Stream 955, comprising 3PN and 2M3BN, may be transferred at least inpart to distillation apparatus 960. In this apparatus, the distillationof stream 955 occurs to obtain 2M3BN-enriched stream 967 and a2M3BN-depleted stream 300 comprising 3PN. Stream 967 may be obtained atthe top region of the distillation apparatus, while the stream 300 maybe obtained at the bottom region of the distillation apparatus.

FIG. 5 illustrates one distillation system for distilling the effluentfrom the second reaction zone (Z₂). However, it will be understood thatit is within the skill in the art to design and operate otherdistillation systems to achieve the same or essentially the sameresults. For example, a distillation step to remove low boilers may beinserted into the system, as described above. It is also possible toshare equipment used for distilling the effluent from the first reactionzone. For example, a stream comprising 3PN and 2M3BN obtained bydistilling the effluent from the second reaction zone (Z₂) may be passedto a distillation apparatus, such as distillation apparatus 830, used inthe distillation of the effluent form the from the first reaction zone(Z₁), to obtain a 3PN-enriched stream and a 2M3BN-enriched stream.

Comparison of Example 1 and Example 2 Lewis acid in the Catalyst of theFirst (Z₁) and Second (Z₂) Reaction Zones

The residual Lewis acid concentration in the catalyst of the first (Z₁)and second (Z₂) zones increases in Example 1. The physical state of theLewis acid in the catalyst does not appear to be critical, and may bepresent in the catalyst in solution or by entrainment. The presence ofthe Lewis acid is observed to correlate with increased conversion of1,3-butadiene to MGN in the first reaction zone (Z₁). This initialconversion of 1,3-butadiene to MGN results in loss of ADN yield.

Example 3 Segregated Catalyst Recovery Systems

Example 3 illustrates partially segregated catalyst recovery systemswith monodentate ligand in the Z₁/Z₂ catalyst loops and bidentate ligandin the Z₃ catalyst loop where the Z₁ and Z₂ catalyst loops share a firstcatalyst recovery section and the Z₃ catalyst loop has a dedicatedsecond catalyst recovery system. In this Example 3, the Z₁/Z₂ catalystrecovery section and the Z₃ catalyst recovery section are segregated tominimize flow of the monodentate ligand of Z₁/Z₂ into the bidentateligand of Z₃, and the bidentate ligand and Lewis acid of Z₃ into themonodentate ligand of Z₁/Z₂.

For this Example 3, Example 2 is repeated, except that the firstreaction zone (Z₁) and the second reaction zone (Z₂) share a singlecatalyst recovery system, not shown in FIG. 1. A shared catalystrecovery system may be desirable when the first and secondphosphite-containing ligands are the same, as is the case in thisExample 3, where both Z₁ and Z₂ use a catalyst comprising a monodentatephosphite ligand. In such a shared system, the following features may beeliminated or shut down: lines 226, 230, 234, 247, 248, 700, and 710;extraction zone 250; distillation apparatus 255; and separation section2000. Instead of taking a purge stream via line 226, a purge stream maybe taken via line 227 and introduced into line 126 or directly intoextraction zone 150. In such a shared catalyst recovery system, anypartially purified catalyst stream entering the second reaction zone(Z₂) would pass through lines 246 and 240 according to the configurationshown in FIG. 1.

Comparison of Example 2 and Example 3

In comparison with Example 2, the substitution of the monodentate ligandcoupled with isolating the Z₁/Z₂ catalyst recovery section from the Z₃catalyst recovery section lowers the production of C₉ mononitriles fromthe first reaction zone (Z₁) by about 0.3% per pass, based on1,3-butadiene feed. These C₉ mononitriles readily convert to C₁₀dinitriles (also referred to as decenedinitriles or DDNs) in the thirdreaction zone (Z₃), degrade the quality of the as-produced ADN andresult in ADN yield loss from 1,3-butadiene.

Example 3 also lowers the formation of VCH (vinylcyclohexane) in thefirst reaction zone (Z₁) by about 0.5% per pass in comparison withExample 2. This is desirable because converting 1,3-butadiene to VCH(rather than to 3-pentenenitrile and then further to adiponitrile)represents a yield loss of ADN.

Example 3 lowers production of undesired byproducts from the firstreaction zone (Z1), especially including 2-pentenenitrile, by about1.0%. This is significant because 2-pentenenitriles in the reaction zone(Z₁) outlet carry through both the second isomerization reaction zone(Z₂) without substantially reacting to 3-pentenenitriles, and then carrythrough the third hydrocyanation zone (Z₃) without substantiallyreacting to form ADN. Thus 1,3-butadiene converted to 2-pentenenitrileis a yield loss with respect to ADN.

Using a monodentate phosphite ligand (rather than a bidentate phosphiteligand) in the first and second reaction zones (Z₁ and Z₂) allows themaximum temperatures in distillation apparatus 810 to be increased. Thiseliminates the need for vacuum operation, thus improving safety andreliability of the butadiene recovery steps.

Example 4 through 7 Removing TBC

The following Examples 4 through 7 illustrate methods for removing TBCfrom 1,3-butadiene. Removing TBC from the 1,3-butadiene feed to thefirst reaction zone (Z₁) reduces formation of undesired byproductsgenerated by the reaction of TBC with the phosphite ligand present inZ₁.

Example 4

In Example 4, three commercial 1,3-butadiene feeds are separately andsequentially charged to the first reaction zone (Z₁). The threecommercial 1,3-butadiene feeds contain 50, 100 and 500 ppm of TBC(tert-butylcatechol). For comparison, the feed containing 50 ppm TBC iscontacted with a suitable sorbent such as activated carbon or activatedalumina to extract the essentially all the TBC from the 1,3-butadienefeed, thus providing the feed for Comparative Example 4, containing lessthan about 1 ppm (weight) of TBC. Any suitable sorbent may be used inthis Example 4, as is known to those of ordinary skill in the art.

Process Process configuration of configuration of Example 2 - Example3 - Bidentate Monodentate Ligand in First Ligand in First Reaction ZoneReaction Zone (Z₁) - Weight (Z₁) - Weight percent of Z₁/Z₂ percent ofZ₁/Z₂ catalyst catalyst TBC content, inventory lost to inventory lost toppm (weight) TBC reaction TBC reaction based on 1,3- products perproducts per butadiene feed unit time. unit time. Comparative <1 0 0Example 4 Example 4a 50 10 1 Example 4b 100 20 2 Example 4c 500 100 10

Example 5 Flashing 1,3-butadiene to Remove TBC

Example 5 illustrates a first of two methods for removal of TBC from1,3-butadiene feed.

1,3-butadiene is charged to a flash drum at near-atmospheric pressure.Heat input to the flash drum is approximately 417.8 kJ/kg of1,3-butadiene feed. TBC is drawn off as a bottoms product. The1,3-butadiene is then cooled and condensed before flowing the purified1,3-butadiene to the first reaction zone (Z₁).

Example 6 Caustic Wash to Remove TBC

1,3-butadiene is flashed and charged to a lower inlet of acountercurrent gas-liquid contactor while an aqueous NaOH solution ischarged to the top of the contactor through a liquid distributor. Thepurified, wet 1,3-butadiene overhead stream is then charged to amulti-bed molecular sieve dryer piped and valved in parallel to allowselective sorption and regeneration. Dry nitrogen or dry flare gas isback-charged through the molecular sieve beds for regeneration. Thedried, caustic-washed 1,3-butadiene contains less than about 5 ppm TBC.

Example 7 Direct Sorption to Remove TBC

Liquid 1,3-butadiene is charged to a first of two sorption bedscontaining an activated carbon sorbent as taught in U.S. Pat. No.4,547,619 to Diaz. As described for the molecular sieve dryer of Example6, the activated carbon sorption beds are piped and valved in parallelto allow selective sorption and regeneration. As needed, the sorbentbeds are selectively regenerated by heating or by passing a heatednon-oxidizing gas, such as nitrogen or superheated steam, through thesorption bed. The flow of commercially delivered 1,3-butadiene throughthe sorbent bed is controlled to provide a purified 1,3-butadieneintermediate product stream containing less than about 5 ppm TBC.

Example 8 Production of Vinylcyclohexane (VCH)—Normal Unit Operation

Examples 2 and 3 are repeated and VCH formation is monitored. VCH is anundesired byproduct of the first reaction zone (Z₁). VCH is a cyclicdimerization product formed by 1,3-butadiene and thus represents a yieldloss of adiponitrile. During normal continuous operation, the VCHcontent of the crude reaction product of the first reaction zone (Z₁) ofExample 2 is measured and compared with the VCH content of the crudereaction product of the first reaction zone (Z₁) of Example 3. VCHformation in the Example 2 crude pentenenitrile product stream is about1% higher than that of Example 3.

Example 9 Production of Vinylcyclohexane (VCH)—Startup and Shutdown UnitOperation

Example 8 is repeated during unit startup and unit shutdown. During unitstartup and shutdown, 1,3-butadiene recycle is increased, due in part tolower per-pass conversions and also by design to stabilize unitoperations. VCH production increases as a function of contact timebetween the catalyst of the first reaction zone and the 1,3-butadiene,with VCH formation in the Example 3 (monodentate ligand in Z₁ and Z₂,bidentate ligand in Z₃) process configuration consistently being lowerthan that of the Example 2 configuration (bidentate ligand in all of Z₁,Z₂ and Z₃ reaction zones).

Example 10 Removal of C₉ Mononitriles

This Example 10 illustrates the building up of C₉ mononitriles in anintegrated catalyst recovery/regeneration loop. Example 1 is repeatedand the concentration of C₉ mononitriles is measured at the outlet ofthe first reaction zone (Z₁). Concentrations vary during the run,ranging from about 1000 ppm to about 10,000 ppm based on total reactionzone effluent. Using the integrated catalyst purification system ofExample 1, the C₉ mononitriles accumulate in the catalyst loop. As theconcentration of C₉ mononitriles builds in the catalyst loop, these C₉mononitriles are at least partially transferred into the3-pentenenitrile-enriched feed to the third reaction zone (Z₃), wherethey readily convert to DDNs and degrade the quality of the crudeas-produced dinitrile product.

Example 11 Removal of C₉ Mononitriles with Segregated Catalyst RecoverySystems

Example 3 is repeated.

Stream 126 has a higher concentration of (is enriched in) C₉mononitriles relative to the effluent from the first reaction zone (Z₁).These C₉ mononitriles proportion between the raffinate and extractphases in the liquid/liquid extraction system. The raffinate is chargedthrough line 510 and 515 to the first column K₁ of separation section1000. The C₉ mononitriles concentrate in the K₁ bottoms stream 520 wherethey are charged to column K₂. Column K₂ is operated such a majority ofthe C₉ mononitriles leave the column in the bottoms stream 530, wherethey flow to column K₃ and exit via 535, then via 420 from column K₄.

Example 12 Removal of C9 Mononitriles with MGN

Example 3 is repeated.

This Example 12 illustrates that the removal of MGN, C9 mononitriles,phenol and cresols from the reaction system, ultimately through thedistillation train used to treat the raffinate stream from theextractor, may be facilitated by distilling the reaction product streamfrom the first reaction zone (Z₁) in a particular manner. For example,after removing unreacted 1,3-butadiene and hydrogen cyanide from thereaction product stream 122 via distillation apparatus 810 as shown inFIG. 4, distillation apparatus 820 receives the bottoms stream(substantially free of 1,3-butadiene in this Example 12) fromdistillation apparatus 810 and is controlled to concentrate C₉mononitriles in the bottoms stream 140. Distillation apparatus 820 iscontrolled by selecting the number of stages in the rectificationsection and the reflux ratio to concentrate C₉ mononitriles in thebottoms stream 140. The distillation apparatus 820 is operated in amanner such that the catalyst-enriched stream comprises at least 5% byweight of pentenenitrile including the sum of 3-pentenenitrile and2-methyl-3-butenenitrile. In this way, MGN, C₉ mononitriles, phenol andcresols tend to pass into the catalyst-enriched stream.

These compounds may then be removed from bottoms stream 140, andaccordingly, at least in part from the reaction system, by aliquid/liquid extraction process, as described above.

The process conditions in distillation apparatus 820 can be adjusted toincrease the relative concentration of pentenenitriles in the bottomsstream 140, thus decreasing the relative concentration of C₉mononitriles in the overhead stream 824. This tends to improve removalof C₉ mononitriles from the system.

About 90% by weight of the C₉ mononitriles present in the raffinate fromthe catalyst recovery system associated with the first reaction zone(Z₁) are removed in the overhead stream of column K₄. Conditions indistillation apparatus 820 are adjusted to provide C₉ mononitrileconcentration in the charge to the third reaction zone (Z₃) of less than1500 ppm, for example less than 1000, less than 500 ppm, or less than100 ppm depending upon the purity requirements for the as-produceddinitrile effluent from the third reaction zone (Z₃).

Example 13 Enhanced Removal of C₉ Mononitriles—Chimney Tray Side DrawColumn

Example 12 is repeated.

This Example 13 illustrates enhanced removal of C₉ mononitriles using aparticular tray and pumparound configuration for the bottom tray ofdistillation apparatus 820 of FIG. 4, included in separation section 125in FIG. 1.

One of the problems attendant to recycling catalyst to the firstreaction zone (Z₁) is that dinitriles formed in the first reaction zone(Z₁) tend to build up in the catalyst recycle loop. This problem is atleast partially mitigated by installing a chimney tray in thepentenenitrile separation column, referred to here as distillationapparatus 820.

For this Example 13, distillation apparatus 820 in FIG. 4 is fitted witha chimney tray.

This distillation apparatus 820 in FIG. 4 is illustrated with a chimneytray as distillation apparatus 850 in FIG. 6.

The chimney tray 870 is located at a point just above the feed inlet852. Liquid accumulates on the chimney tray and is drawn off via line872 and pump 874, charged via line 876 to trim heater 880 with capacitysufficient to vaporize at least part of the feed to the trim heater. Theheated stream 882 is then returned to the chimney tray 870 or at a pointalong the distillation apparatus 850 just above the chimney tray 870,

A catalyst-enriched liquid accumulates in the bottom section ofdistillation apparatus 850, and is heated by a reboiler 866. Above thechimney tray 870, the pentenenitrile separation column may contain oneor more stages of separation in the form of trays or packing 854. Theoverhead stream 856 may be partially condensed and the liquid refluxedto the top of the distillation apparatus 850.

The side draw stream 878 downstream from pump 874 is enriched in C₉mononitriles and dinitriles. This process configuration of Example 13reduces the C₉ mononitrile and dinitrile content of the recycledcatalyst stream to the first reaction zone (Z₁) and provides a streamconcentrated in C₉ mononitriles and dinitriles for more effectivelyremoving these components from the process upstream of the thirdreaction zone (Z₃). By operating this chimney tray side drawconfiguration of Example 13, flow of C₉ mononitriles and dinitriles tothe third reaction zone (Z₃) is reduced.

Example 14 Comparison of C₉ Mononitrile formation in Examples 2 and 3

Examples 2 and 3 are repeated, and the total production of C₉mononitriles from the first reaction zone (Z₁) is measured.

In Example 3, the catalyst comprising the monodentate ligand produces amixed pentenenitrile product from the first reaction zone (Z₁)containing about 500 ppm of C₉ mononitriles. In Example 2, the catalystcomprising the bidentate ligand produces a mixed pentenenitrile productfrom the first reaction zone (Z₁) containing from about 1000 to 10000 ormore ppm of C₉ mononitriles.

Example 15 Dedicated 3-Pentenenitrile Distillation

This Example 15 illustrates another option to reduce the concentrationof C₉ mononitriles in the feed to the third reaction zone (Z₃).

One method to reduce the content of C₉ mononitriles in the3-pentenenitrile feed to the third reaction zone (Z₃) is to modify theoperation of Example 2 by distilling the 3-pentenenitrile feed stream toprovide an overhead stream enriched in 3-pentenenitrile and a bottomsstream enriched in C₉ mononitriles.

The 3-pentenenitrile product from the first reaction zone (Z₁), andoptionally isomerized pentenenitrile effluent (“isomerate”) from thesecond reaction zone (Z₂), is charged to a multistage distillationcolumn equipped with an overhead condenser and return piping with one ormore control valves for adjusting column pressure and reflux ratio. Themultistage distillation column also includes one or more reboilers andoptional interstage heaters below the feed point for vaporizing liquidin the column. The column operation is controlled to provide an overheadstream enriched in 3-pentenenitrile and a bottom stream enriched in C₉mononitriles and dinitriles including MGN. Energy input to this columnfor flashing, cooling and condensing essentially all of the3-pentenenitrile effluent from the second reaction zone (Z₂)significantly increases the total energy consumption per unit time ofthe ADN process in comparison to Examples 2 and 3 operated without thisadditional distillation step.

Example 16 Enhanced Removal of Intermediate Boilers

In this Example 16, Example 13 is repeated.

Example 16 illustrates enhanced removal of intermediate boilers, such asMGN, C₈H₁₃C≡N compounds, phenol and cresols from the reaction system,ultimately through the distillation and liquid/liquid separationsections by selectively treating stream 878 withdrawn from distillationapparatus 850 as shown in FIG. 6.

These compounds may then be removed at least in part from the reactionsystem by the extraction process into the raffinate and from theraffinate by the raffinate treatment process described above. The streamfrom the side draw 878 may then be passed either directly or indirectly(e.g., into the catalyst purge stream) to the extraction section. Inthis way, there is achieved an increased amount of MGN, C₈H₁₃C≡Ncompounds, phenol and cresols passed into the extraction section andseparated from recycled catalyst. Optionally, stream 878 can be fed to amultistage extraction section after the first stage of the multistageextraction section to further improve C₉ mononitrile rejection.

Example 17 TBC Byproducts

This Example 17 illustrates the behavior of tertiary-butylcatechol (TBC)in the disclosed process.

Tertiary-butylcatechol (TBC) is a polymerization inhibitor, whichinhibits the polymerization of 1,3-butadiene, particularly while the1,3-butadiene is in storage. Commercial sources of 1,3-butadiene ofteninclude small amounts of TBC to inhibit polymerization of 1,3-butadiene.

TBC reacts with monodentate phosphite ligands and bidentate phosphiteligands.

TBC in the 1,3-butadiene feed triggers a number of problems. TBC reactswith ligand in the first reaction zone (Z₁) to form TBC byproducts whichcomplex with nickel and TBC byproducts which react with catalystligands. These nickel-containing complexes appear to be lesscatalytically active than the nickel-ligand complex of the firstcatalyst. Reactive TBC byproducts of the TBC reaction in the firstreaction zone (Z₁) further include compounds, such as phenol andcresols, which may further react with catalyst ligand in the thirdreaction zone (Z₃). The reaction of these reactive TBC byproducts withcatalyst ligand in the third reaction zone (Z₃) causes similar problemsin that new nickel-containing complexes are generated. These newlygenerated nickel-containing complexes are less catalytically active thanthe nickel-ligand complex of the third catalyst. As described below, aportion of the reactive TBC byproducts is rejected into the raffinatephase of a liquid/liquid extraction section and removed from theprocess.

Examples 2 and 3 are repeated. The reactive TBC byproducts (e.g., phenoland cresols) described above are withdrawn from the K₄ column of FIG. 2as overheads. This withdrawal through the K₄ column is made possible byoperating the pentenenitrile separation column (K₂) to keep most of theTBC byproducts out of the pentenenitrile separation column overheads.

Example 18 Ligand Hydrolysis Products

Example 2 is repeated. The catalyst in the first, second and thirdreactions zones (Z₁, Z₂ and Z₃) contains a bidentate phosphite ligand.

A portion of the bidentate ligand in the first reaction zone (Z₁)catalyst loop reacts with water to form light ligand hydrolysis product(LLHP) and heavy ligand hydrolysis product (HLHP). The purge from thecatalyst loop is contacted in the extraction system. The raffinate(polar) phase from the extraction system is charged to separationsection 1000. The LLHP is removed from the system via the overheads 420of K₄ and the HLHP is removed from the system via line 540 from K₃.

Example 19 Removal of Ligand Hydrolysis Products

Example 3 is repeated. The catalyst in the first and second reactionzones (Z₁ and Z₂) contains a monodentate phosphite ligand and thecatalyst in the third reaction zone (Z₃) contains a bidentate phosphiteligand.

A portion of the bidentate ligand in the first reaction zone (Z₁)catalyst loop reacts with water to form light ligand hydrolysis product(LLHP) and heavy ligand hydrolysis product (HLHP). The purge from thecatalyst loop is contacted in the extraction system.

The raffinate (polar) phase from the extraction system is charged toseparation section 1000. The LLHP is removed from the system via theoverheads 420 of K₄ and the HLHP is removed from the system via line 540from K₃.

Example 20 Removal of MGN Through Liquid-Liquid Extraction

Example 3 is repeated. The crude product of the first reaction zoneprincipally contains pentenenitriles and unreacted 1,3-butadiene, butalso contains a minor portion of dinitriles including adiponitrile (ADN)and methylglutaronitrile (MGN).

The catalyst flowing from the first reaction zone (Z₁) or the secondreaction zone (Z₂) or both the first and second reaction zone isconcentrated in one or more distillation columns and recycled in atleast one catalyst recycle stream to the first reaction zone (Z₁) or thesecond reaction zone (Z₂) or both the first and second reaction zone (Z₁and Z₂).

At least a portion of the catalyst recycle stream is contacted with anextraction solvent in a liquid/liquid extraction step to produce asolvent phase and a raffinate phase. The solvent phase comprisesextraction solvent and catalyst and the raffinate phase comprises thedinitrile compounds comprising MGN, compounds with a higher boilingpoint than the dinitrile compounds and compounds with a lower boilingpoint than the dinitrile compounds. The catalyst from the solvent phaseobtained in the liquid/liquid extraction step is then recycled to thefirst reaction zone or the second reaction zone or both the first andsecond reaction zone.

Example 21 Isolating the First and Second Reaction Zones from the LewisAcid of the Third Reaction Zone

Example 3 is repeated except that ZnCl₂ (Lewis acid) from the thirdreaction zone Z₃ is charged back to the first reaction zone (Z₁). Thecrude product from the first reaction zone (Z₁) is continuouslymonitored for dinitrile content. Several minutes after the control valveis partially opened to charge the Lewis acid from the third reactionzone back to the first reaction zone at a concentration of about 100 ppmof zinc, based on total catalyst charged to the first reaction zone, thecontrol valve is opened further to increase the zinc charge to the firstreaction zone to about 500 ppm. At 100 ppm zinc, the crude productcontains about 0.5% by weight MGN. Increasing the Lewis acid charge to500 ppm increases the production of MGN to about 1.0% by weight of crudeproduct from the first reaction zone (Z₁).

Example 22 Zinc Chloride in the Extraction Solvent

Example 1 is repeated. The cyclohexane extraction from the sharedcatalyst extraction system is analyzed for Zn as taught in U.S. Pat. No.3,778,809 to Walter.

About 100 ppm of Zn in the recycled catalyst correlates with about 0.8%MGN yield. Increasing the Zn level in the recycled catalyst by another100 ppm increases the MGN yield by another 0.5% for a total of 1.3%(weight).

Example 23

In this Example 23, adiponitrile is produced by the two-stephydrocyanation of 1,3-butadiene by reacting in a first reaction zone amixture comprising 1,3-butadiene (BD) and hydrogen cyanide (HCN) in thepresence of a first catalyst comprising zero-valent Ni and a firstphosphorus-containing ligand to produce a reaction product comprising3-pentenenitrile (3PN) and 2-methyl-3-butenenitrile (2M3BN).

At least a portion of the 2M3BN formed as byproduct is isomerized in asecond reaction zone in the presence of a second catalyst comprisingzero-valent Ni and a second phosphorus-containing ligand to producereaction product comprising 3PN.

The catalyst flows through the first and second reaction zones alongwith reactants and products.

The zero valent nickel content of the catalyst is reduced and catalystdegradation byproducts are produced during the process.

Catalyst flowing from the first reaction zone is concentrated in one ormore distillation steps and recycled to the first reaction zone.

A portion of the concentrated first catalyst is purified by removingcatalyst degradation products in a liquid/liquid extraction step.

The purified first catalyst is recycled to the first reaction zone orthe second reaction zone or both the first and second reaction zone.

Zero valent nickel is added to the purified catalyst from theliquid/liquid extraction step after the catalyst is purified in theliquid/liquid extraction step and before the purified catalyst isrecycled to the first reaction zone or the second reaction zone or boththe first and second reaction zone.

The desired mononitrile, isomerate and dinitrile products are recoveredfrom each reaction zone, respectively.

Example 24

The process of Example 23 is repeated and no zero valent nickel is addedto the concentrated catalyst feed to a liquid/liquid extraction step.

The desired mononitrile, isomerate and dinitrile products are recoveredfrom each reaction zone, respectively.

Example 25

The process of Example 23 is repeated with the additional steps ofreacting in a third reaction zone a mixture comprising 3PN from theisomerization zone and hydrogen cyanide (HCN) in the presence of a thirdcatalyst comprising zero-valent Ni and a third phosphorus-containingligand and in the presence of Lewis acid promoter to produce a reactionproduct comprising adiponitrile.

In Example 25, catalyst flows through the first, second and thirdreaction zones along with reactants and products.

The desired mononitrile, isomerate and dinitrile products are recoveredfrom each reaction zone, respectively.

Example 26

The process of Example 23 is repeated.

In this Example 26, the liquid/liquid extraction step includesintroducing a portion of the concentrated first catalyst, an extractionsolvent and dinitriles into a first liquid/liquid extractor. Next, theliquids are separated in the liquid/liquid extractor into a solventphase comprising catalyst and a raffinate phase comprising dinitrilesand catalyst degradation products.

The desired mononitrile, isomerate and dinitrile products are recoveredfrom each reaction zone, respectively.

Example 27

The process of Example 26 is repeated.

The solvent phase from the liquid/liquid extractor is distilled toremove extraction solvent and to obtain a purified catalyst stream.

The desired mononitrile, isomerate and dinitrile products are recoveredfrom each reaction zone, respectively.

Example 28

The process of Example 27 is repeated.

Zero valent nickel is added to the purified catalyst stream and thepurified catalyst stream is recycled to the first reaction zone.

The desired mononitrile, isomerate and dinitrile products are recoveredfrom each reaction zone, respectively.

Example 29

The process Example 26 is repeated.

The raffinate phase comprises extraction solvent, pentenenitriles,dinitriles and catalyst degradation products, wherein extractionsolvent, pentenenitriles, dinitriles and catalyst degradation productsare separated from one another, and dinitriles are recycled to theliquid/liquid extraction step.

The desired mononitrile, isomerate and dinitrile products are recoveredfrom each reaction zone, respectively.

Example 30

The process of Example 25 is repeated.

The second reaction zone and the third reaction zone are separated fromeach other by a distance of at least 500 meters.

The second reaction zone and the third reaction zone are capable ofbeing operated separately and independently from each other.

Example 31

The process of Example 23 is repeated.

In this Example 31, the first phosphorus-containing ligand is amonodentate phosphorus-containing ligand, and the secondphosphorus-containing ligand is a monodentate phosphorus-containingligand or a bidentate phosphorus-containing ligand.

The desired mononitrile, isomerate and dinitrile products are recoveredfrom each reaction zone, respectively.

Example 32

The process of Example 31 is repeated.

The second phosphorus-containing ligand is a monodentatephosphorus-containing ligand, and the first phosphorus-containing ligandand the second phosphorus-containing ligand are the same.

The desired mononitrile, isomerate and dinitrile products are recoveredfrom each reaction zone, respectively.

Example 33

The process of Example 26 is repeated. The first phosphorus-containingligand is a monodentate phosphorus-containing ligand, the secondphosphorus-containing ligand is a monodentate phosphorus-containingligand.

The first phosphorus-containing ligand and the secondphosphorus-containing ligand are the same.

The third phosphorus-containing ligand is a bidentatephosphorus-containing ligand.

The desired mononitrile, isomerate and dinitrile products are recoveredfrom each reaction zone, respectively.

Example 34

The process of Example 26 is repeated.

The process includes at least two separate liquid/liquid extractionsteps for the catalyst. The third catalyst flowing from the thirdreaction zone is contacted with an extraction solvent in a separateliquid/liquid extraction step. This separate liquid/liquid extractionstep is different from the liquid/liquid extraction step used to purifythe first catalyst.

The third catalyst is recovered from the separate liquid/liquidextraction step and recycled to the third reaction zone, but not to thefirst reaction zone.

In each example, the first phosphorus-containing ligand is TTP or MTTP,and the third phosphorus-containing ligand is a bidentatephosphite-containing ligand. Tertiary-butylcatechol reacts with TTP orMTTP to produce catalyst degradation products comprising cresols. Theraffinate phase of the liquid/liquid extraction step comprises cresols.The raffinate phase is distilled to remove cresols.

Example 35

The process of Example 23 is repeated.

This Example 35 uses at least two separate liquid/liquid extractionsteps.

The second catalyst flowing from the second reaction zone is contactedwith an extraction solvent in a separate liquid/liquid extraction step,which is different from the liquid/liquid extraction step used to purifythe first catalyst.

The second catalyst is recovered from the separate liquid/liquidextraction step and recycled to the second reaction zone, but not to thefirst reaction zone.

The first catalyst is recovered from a liquid/liquid extraction step andrecycled to the first reaction zone, but not to the second reactionzone.

The desired mononitrile, isomerate and dinitrile products are recoveredfrom each reaction zone, respectively.

Example 36

The process of Example 23 is repeated.

The first phosphorus-containing ligand and the secondphosphorus-containing ligand are the same.

The second catalyst flowing from the second reaction zone is contactedwith an extraction solvent in the same liquid/liquid extraction stepused to purify the first catalyst.

Catalyst is recovered from the liquid/liquid extraction step andrecycled to both the first and second reaction zone.

The desired mononitrile, isomerate and dinitrile products are recoveredfrom each reaction zone, respectively.

It should be noted that ratios, concentrations, amounts, and othernumerical data may be expressed herein in a range format. It is to beunderstood that such a range format is used for convenience and brevity,and thus, should be interpreted in a flexible manner to include not onlythe numerical values explicitly recited as the limits of the range, butalso to include all the individual numerical values or sub-rangesencompassed within that range as if each numerical value and sub-rangeis explicitly recited. To illustrate, a concentration range of “about0.1% to about 5%” should be interpreted to include not only theexplicitly recited concentration of about 0.1 wt % to about 5 wt %, butalso the individual concentrations (e.g., 1%, 2%, 3%, and 4%) and thesub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicatedrange. The term “about” can include ±1%, ±2%, ±3%, ±4%, ±5%, ±8%, or±10%, of the numerical value(s) being modified. In addition, the phrase“about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”.

While the illustrative embodiments of the invention have been describedwith particularity, it will be understood that the invention is capableof other and different embodiments and that various other modificationswill be apparent to and may be readily made by those skilled in the artwithout departing from the spirit and scope of the invention.Accordingly, it is not intended that the scope of the claims hereof belimited to the examples and descriptions set forth herein but ratherthat the claims be construed as encompassing all the features ofpatentable novelty which reside in the present disclosure, including allfeatures which would be treated as equivalents thereof by those skilledin the art to which the invention pertains.

What is claimed is:
 1. A process for making 3-pentenenitrile, saidprocess comprising the steps of: (a) reacting in a first reaction zone amixture comprising 1,3-butadiene (BD) and hydrogen cyanide (HCN) in thepresence of a first catalyst comprising zero-valent Ni and a firstphosphorus-containing ligand to produce a reaction product comprising3-pentenenitrile (3PN) and 2-methyl-3-butenenitrile (2M3BN); (b)isomerizing at least a portion of the 2M3BN of step (a) in a secondreaction zone in the presence of a second catalyst comprisingzero-valent Ni and a second phosphorus-containing ligand to producereaction product comprising 3PN; wherein first catalyst flows throughthe first reaction zones along with reactants and products, whereinsecond catalyst flows through the second reaction zones along withreactants and products, wherein the zero valent nickel content of thefirst catalyst is reduced and catalyst degradation byproducts areproduced during the process, wherein first catalyst flowing from thefirst reaction zone is concentrated in one or more distillation steps toform a concentrated first catalyst and recycled to the first reactionzone, wherein a portion of the concentrated first catalyst is purifiedby removing catalyst degradation products in a liquid/liquid extractionstep to form a purified catalyst, wherein the purified first catalyst isrecycled to the first reaction zone or the second reaction zone or boththe first and second reaction zone, wherein zero valent nickel is addedto the purified catalyst from the liquid/liquid extraction step afterthe catalyst is purified in the liquid/liquid extraction step and beforethe purified catalyst is recycled to the first reaction zone or thesecond reaction zone or both the first and second reaction zone, andwherein the zero valent nickel added to the purified catalystreplenishes first catalyst which has been lost by degradation during theprocess.
 2. The process of claim 1, wherein no zero valent nickel isadded to the concentrated first catalyst prior to the liquid/liquidextraction step.
 3. The process of claim 1, wherein the liquid/liquidextraction step comprises introducing a portion of the concentratedfirst catalyst, an extraction solvent and dinitriles into a firstliquid/liquid extractor, and separating liquids in the liquid/liquidextractor into a solvent phase comprising first catalyst and a raffinatephase comprising dinitriles and catalyst degradation products.
 4. Theprocess of claim 3, wherein the solvent phase from the liquid/liquidextractor is distilled to remove extraction solvent and to obtain apurified catalyst stream.
 5. The process of claim 4, wherein zero valentnickel is added to the purified catalyst and the purified catalyst isrecycled to the first reaction zone.
 6. The process of claim 3, whereinthe raffinate phase comprises extraction solvent, pentenenitriles,dinitriles and catalyst degradation products, wherein extractionsolvent, pentenenitriles, dinitriles and catalyst degradation productsare separated from one another, and dinitriles are recycled to theliquid/liquid extraction step.
 7. The process of claim 1, wherein thefirst phosphorus-containing ligand is a monodentatephosphorus-containing ligand, and wherein the secondphosphorus-containing ligand is a monodentate phosphorus-containingligand or a bidentate phosphorus-containing ligand.
 8. The process ofclaim 7, wherein the second phosphorus-containing ligand is amonodentate phosphorus-containing ligand, and wherein the firstphosphorus-containing ligand and the second phosphorus-containing ligandare the same.
 9. The process of claim 1 comprising at least two separateliquid/liquid extraction steps, wherein said second catalyst flowingfrom the second reaction zone is contacted with an extraction solvent ina separate liquid/liquid extraction step, which is different from theliquid/liquid extraction step used to purify the first catalyst, whereinsaid second catalyst is recovered from the separate liquid/liquidextraction step and recycled to the second reaction zone, but not to thefirst reaction zone, and wherein said first catalyst is recovered from aliquid/liquid extraction step and recycled to the first reaction zone,but not to the second reaction zone.
 10. The process of claim 1, whereinthe first phosphorus-containing ligand and the secondphosphorus-containing ligand are the same, wherein said second catalystflowing from the second reaction zone is contacted with an extractionsolvent in the same liquid/liquid extraction step used to purify thefirst catalyst, and wherein the first and second catalyst is recoveredfrom the liquid/liquid extraction step and recycled to both the firstand second reaction zone.
 11. A process for the production ofadiponitrile comprising a process according to claim 1 furthercomprising the step of (c) reacting in a third reaction zone a mixturecomprising 3PN from step (b) and hydrogen cyanide (HCN) in the presenceof a third catalyst comprising zero-valent Ni and a thirdphosphorus-containing ligand and in the presence of Lewis acid promoterto produce a reaction product comprising adiponitrile, wherein thirdcatalyst flows through the third reaction zone along with reactants andproducts.
 12. The process of claim 11, wherein the second reaction zoneand the third reaction zone are separated from each other by a distanceof at least 500 meters, and wherein the second reaction zone and thethird reaction zone are capable of being operated separately andindependently from each other.
 13. The process of claim 11 wherein thefirst phosphorus-containing ligand is a monodentatephosphorus-containing ligand, wherein the second phosphorus-containingligand is a monodentate phosphorus-containing ligand, wherein the firstphosphorus-containing ligand and the second phosphorus-containing ligandare the same, and wherein the third phosphorus-containing ligand is abidentate phosphorus-containing ligand.
 14. The process of claim 11comprising at least two separate liquid/liquid extraction steps, whereinsaid third catalyst flowing from the third reaction zone is contactedwith an extraction solvent in a separate liquid/liquid extraction step,which is different from the liquid/liquid extraction step used to purifythe first catalyst, and wherein said third catalyst is recovered fromthe separate liquid/liquid extraction step and recycled to the thirdreaction zone, but not to the first reaction zone.
 15. The process ofclaim 1, wherein said first phosphorus-containing ligand and said secondphosphorus-containing ligand are selected from the group consisting of amonodentate or bidentate phosphite ligand, a monodentate or bidentatephosphine ligand, a monodentate or bidentate phosphonite ligand, amonodentate or bidentate phosphinite ligand, and a mixture of theseligands.
 16. The process of claim 11, wherein thirdphosphorus-containing ligand is selected from the group consisting of amonodentate or bidentate phosphite ligand, a monodentate or bidentatephosphine ligand, a monodentate or bidentate phosphonite ligand, amonodentate or bidentate phosphinite ligand, and a mixture of theseligands.
 17. The process of claim 8, wherein said firstphosphorus-containing ligand and said second phosphorus-containingligand is at least one ligand of Formula I, where Formula I isP(OR²)(OR³)(OR⁴)  (I) where R², R³ and R⁴ are the same or different andare aryl groups, where the aryl groups are each optionally substitutedwith up to four alkyl groups, each alkyl group having from 1-4 carbonatoms.
 18. The process of claim 17, wherein R², R³ and R⁴ are the sameor different phenyl or tolyl groups.
 19. The process of claim 18,wherein the phosphorus-containing ligand of Formula I is one or moreligands selected from the group consisting of (o-tolyl-O—)₃P,(p-tolyl-O-)(phenyl-O—)₂P, (m-tolyl-O—) (phenyl-O—)₂P,(o-tolyl-O-)(phenyl-O—)₂P, (p-tolyl-O—)₂(phenyl-O—)P,(m-tolyl-O-)₂(phenyl-O—)P, (o-tolyl-O-)₂(phenyl-O—)P,(m-tolyl-O-)(p-tolyl-O-)(phenyl-O—)P,(o-tolyl-O-)(p-tolyl-O-)(phenyl-O—)P,(o-tolyl-O-)(m-tolyl-O-)(phenyl-O-)P, (p-tolyl-O—)₃P,(m-tolyl-O—)(p-tolyl-O—)₂P, (o-tolyl-O-)(p-tolyl-O—)₂P,(m-tolyl-O-)₂(p-tolyl-O—)P, (o-tolyl-O-)₂(p-tolyl-O—)P,(o-tolyl-O-)(m-tolyl-O-)(p-tolyl-O—)P, (m-tolyl-O—)₃P,(o-tolyl-O-)(m-tolyl-O—)₂P, and (o-tolyl-O-)₂(m-tolyl-O—)P.
 20. Theprocess of claim 11, wherein said Lewis acid promoter is an inorganiccompound or an organometallic compound comprising a cation of a metalselected from the group consisting of scandium, titanium, vanadium,chromium, manganese, iron, cobalt, copper, zinc, boron, aluminum,yttrium, zirconium, niobium, molybdenum, cadmium, rhenium, lanthanum,erbium, ytterbium, samarium, tantalum, and tin.
 21. The process of claim11, wherein said Lewis acid promoter is selected from the groupconsisting of salts of metals having atomic numbers 13, 21-32, 39-50,and 57-80 and compounds of the formula BR′₃ wherein R′ is an alkyl or anaryl radical of up to 18 carbon atoms.
 22. The process of claim 21,wherein said Lewis acid promoter comprises ZnCl₂ or triphenylboron.